Category 6™

Category 4 Chapala On Its Way to Yemen; Texas Gasping after More Record Rain

By: Bob Henson and Jeff Masters , 5:30 PM GMT on October 31, 2015

Tropical Cyclone Chapala, the second strongest storm on record for the Arabian Sea, is holding its own as it continues plowing westward toward Yemen. As of 8:00 am EDT Saturday, Chapala’s top sustained winds were down to 135 mph, at the other end of the Category 4 scale from the peak of 155 mph observed on Friday. After its structure was somewhat disrupted on Friday, perhaps by dry air intruding into its circulation, Chapala appears to be regrouping, with a solid inner core of convection and a distinct eye 10 miles in diameter.


Figure 1. Tropical Cyclone Chapala as seen from the International Space Station at sunset on Halloween evening, October 31, 2015. At the time, Chapala was a Category 4 storm with 135 mph winds. The coast of Oman/Yemen is visible at the bottom of the image. Image credit: Commander Scott Kelly.


Figure 2. Tropical Cyclone Chapala as seen by the MODIS instrument on NASA's Terra satellite on Saturday morning, October 31, 2015. At the time, Chapala was a Category 4 storm with 135 mph winds. Image credit: NASA.

The forecast for Chapala
The biggest change since Friday is a southward departure in Chapala’s track. The cyclone is now heading due west and should continue on that bearing for the next couple of days, with a slight curve to the west-northwest as it approaches Yemen on Monday night. Chapala’s healthy structure may keep dry air at bay for some time, but eventually the cyclone should weaken as it near the Arabian Peninsula and ingests greater amounts of parched desert air. The Joint Typhoon Warning Center brings Chapala onshore in the high tropical-storm-strength range, with sustained winds possibly close to hurricane strength.


Figure 3. Three tropical cyclones are known to have made landfall on the southern coast of Oman and Yemen betwen 1891 and the beginning of modern satellite records (1990). Two of these reached northeast Yemen, in May 1959 and May 1960. Both were rated as “severe cyclonic storms” prior to landfall (solid line), meaning their top 3-minute average wind speeds were at least 48 knots (55 mph). Image credit: Courtesy Dr. Mrutyunjay Mohapatra, Head, Cyclone Warning Division and Regional Specialised Meteorological Centre, India Meteorological Department.


According to NOAA's Historical Hurricanes tool, there have only been six major Category 3 or stronger tropical cyclones recorded in the Arabian Sea (though accurate satellite records go back to just 1990.) The Arabian Sea doesn't get many tropical cyclones since it is small; furthermore, the Southwest Monsoon keeps the tropical cyclone season short, with a short season that lasts from May to early June before the monsoon arrives, then another short season in late October through November after the monsoon has departed. Strong Arabian Sea storms are rare due to high wind shear and copious dry air from the deserts of the Middle East, with just two Category 4 or 5 storms ever recorded--Gonu in 2007 and Phet in 2010. Both cyclones hit Oman after weakening below Category 4 strength.

Landfalling cyclones are even more rare in Yemen. The only one in the post-1990 satellite database is Tropical Depression Three of 2008 (also known as the 2008 Yemen Cyclone), which came on the heels of heavy rains from another storm and resulted in disastrous flooding. According to EM-DAT, the international disaster database, that storm killed 90 people and did $400 million in damage, making it the second worst natural disaster in Yemen's history, behind a June 13, 1996 flood (thanks go to wunderground member TropicalAnalystwx13 for alerting us to this fact.) The India Meteorological Department maintains a database of tropical cyclones in the region going back to 1891 that shows two cyclonic storms reaching the Yemen coast in 1960 and 1961 (see Figure 3).


Figure 4. The port of Al Mukalla. Image credit: Roo72/Wikimedia Commons.


Figure 5. Topography of Yemen. Image credit: Sadalmelik/Wikimedia Commons.

Chapala’s southward track will make it only the second tropical cyclone recorded near the mouth of the Gulf of Aden, which is crossed by roughly 400 ships a week. The adjustment in Chapala’s track could have major implications for Yemen, as it brings the center closer to the 980-year-old settlement of Al Mukalla (also known as Mukalla), a busy port and Yemen’s fifth-largest city (population around 300,000). If Chapala were to pass just south of Al Mukalla, the sharp angle of approach to the coast would accentuate any storm surge. Yemen has been in the grip of a civil war since March, so any landfall near this populated area could intersect with the conflict in hard-to-predict ways. According to an October 30 article from Reuters, ten of Yemen's 22 governorates were assessed as being in an emergency food situation in June, one step below famine on a five-point scale. The assessment has not been updated since then, partly because experts have not managed to get sufficient access to survey the situation. About a third of the country's population, or 7.6 million people urgently require food aid, the The U.N. World Food Programme said (thanks go to wunderground member barbamz for alerting us to this article.)

As it moves ashore, Chapala will slam into steep mountains near the coast, boosting its potential to dump several years’ worth of rain in just a day or two (see Figure 6). The annual average rainfall in Yemen is less than 2” along the immediate coast and less than 5” inland, except along higher terrain, where it can approach 10”. Any landfall near Al Mukalla could result in serious urban flooding (the city straddles a canal that extends to the coast from the adjacent mountainsides).


Figure 6. The 5-day rainfall forecast from the 2 am EDT Saturday, October 31, 2015 run of the HWRF model called for some truly stunning rainfall amounts in the parched desert regions of eastern Yemen: over two feet! Image credit: NOAA/EMC.

Rain-weary Texans deal with another deluge
Yet another round of epic downpours struck the heart of Texas from Friday into Saturday. The focus on Friday morning was the HIll Country and the adjacent San Antonio and Austin metro areas, which suffered through record rain and destructive flooding back in May. The air traffic control center at Austin’s Bergstrom International Airport has been shut down after being inundated with six inches of water on Friday. A Houston center is handling its duties until a temporary facility arrives on Monday. Bergstrom received 5.76” of rain in just one hour, as part of a phenomenal calendar-day total of 14.99” on Friday. That’s more than the site had ever recorded in any prior 14-day period! (Records at Bergstrom go back to 1942. Thanks to Nick Wiltgen at weather.com for this statistic.). The total also came within a hair (0.067%) of reaching the city’s all-time 24-hour record of 15.00”, set at Camp Mabry on September 9, 1921, in association with a Category 1 hurricane that caused severe flooding in the San Antonio area. Further south, Brownsville had its second wettest October day in 128 years of recordkeeping, with 6.55” on Friday beaten only by 9.09” on October 4, 1996, in association with Tropical Storm Josephine. The absence of a tropical cyclone makes this event across central and south Texas all the more remarkable.


Figure 7. Jim Richardson and his wife Jeannette look on as the Blanco River recedes after the flash flood in Wimberly, Texas Friday, Oct. 30, 2015. A fast-moving storm packing heavy rain and destructive winds overwhelmed rivers and prompted evacuations Friday in the same area of Central Texas that saw devastating spring floods. Image credit: Ricardo Brazziell/Austin American-Statesman via AP.


Figure 8. Estimated rainfall between 7:00 am CDT Friday, October 30, and Saturday, October 31. Image credit: NOAA Advanced Hydrologic Prediction Service.


A subsequent round of heavy thunderstorms moved into southeast Texas overnight and into Saturday morning, causing widespread flooding in the Houston area, as well as scattered wind damage perhaps associated with one or more tornadoes. With light rain hanging on at noon CDT Saturday, Houston’s Hobby Airport had received 6.50” for the day, bringing its monthly total to 14.24”. Hobby will fall short of the Houston area’s wettest October on record, 17.64” in 1949, a total largely goosed by a Category 2 hurricane early that month. The front edge of this sprawling area of heavy thunderstorms is now approaching southeast Louisiana, which has also been hammered by heavy rain in October. Baton Rouge had received 10.85” for the month as of Friday, and New Orleans 8.88”. NOAA’s Weather Prediction Center is calling for as much as 5-6” of rain over the area today into Sunday. Baton Rouge has an outside chance of scoring its wettest October on record (17.64”, from 1949; records go back to 1889), as does the Louis Armstrong New Orleans International Airport (13.20” in 1985, in association with Hurricane Juan; records go back to 1946).

Dallas-Fort Worth International Airport racked up another 2.25” from Friday through 11:00 am CDT Saturday. The airport has now recorded 48.92” for the year, making 2015 the sixth wettest year since DFW-area records began in 1898. One of the most reliable U.S. impacts from El Niño is increased cold-season rainfall from Texas to Florida. Given the strong El Niño influence already at hand, DFW has a good chance over the next two months of topping 53.54” (1991) to score its wettest year on record. In fact, it could happen quite soon: WPC is projecting 2” to 5” of rain across central North Texas late next week, as another strong Pacific upper-level storm carves its way into the western U.S. That storm will give the Pacific Northwest a seasonally heavy drenching this weekend, and it may leave the first significant accumulation of the season along the snow-starved Sierra Nevada on Monday and Tuesday--perhaps as much as a foot on the highest peaks. A winter storm watch has been hoisted for the region, but we’re guessing most residents will be elated rather than spooked by this October 31 development. Have a great Halloween weekend, everyone!

Bob Henson and Jeff Masters



Video 1. This powerful video was taken by a motorist in central Texas on Friday morning, October 30, 2015, shortly before he awaited rescue. Once a car is afloat in moving water, it will generally flow toward the deepest, fastest-moving areas. According to NOAA, it only takes two feet of moving water to float most vehicles. Image credit: KVUE News.


Video 2. Technician Derek Urch from NWS/Brownsville captured this lightning strike of the WSR-88D Radar, which knocked radar data out completely during a flash flood event on Friday, October 30, 2015. Image credit: NWS/Brownsville.


Hurricane Flood Extreme Weather

2nd Strongest Storm in Arabian Sea History: Extraordinary Chapala Hits 155 mph

By: Jeff Masters and Bob Henson , 4:14 PM GMT on October 30, 2015

Tropical Cyclone Chapala took advantage of the the warmest waters ever recorded in the Arabian Sea at this time of year to put on a remarkable burst of rapid intensification overnight. Chapala topped out for the time being as a top-end Category 4 storm with 155 mph winds (1-minute average) at 2 am EDT Friday, according to the Joint Typhoon Warning Center (JTWC). The India Meteorology Department (IMD), which has official responsibility for tropical cyclone warnings in the North Indian Ocean, put Chapala's intensity at 130 mph winds (3-minute average) with a central pressure of 942 mb at 8 am EDT Friday. This made Chapala the second strongest tropical cyclone on record in the Arabian Sea, behind Category 5 Cylcone Gonu of 2007, the only Category 5 storm ever recorded in the Arabian Sea. Gonu peaked at 165 mph winds (JTWC) or 146 mph (IMD) with a 920 mb pressure. The North Indian Ocean as a whole has seen five Category 5 storms in recorded history (with four of them occurring in the Bay of Bengal), so Chapala is the sixth strongest tropical cyclone ever observed in the North Indian Ocean.


Figure 1. Tropical Cyclone Chapala as seen by the MODIS instrument at 09:10 UTC October 30, 2015. At the time, Chapala was at peak strength with 155 mph winds. Note the large cloud of pollution at the right of the image over India. Image credit: NASA.


Figure 2. Tropical Cyclone Chapala performed its remarkable rapid intensification cycle over the warmest waters ever observed for this time of year over the Arabian Sea, as depicted in the September 2015 global climate summary from NOAA/NCEI.

Strong Arabian Sea tropical cyclones are uncommon
According to NOAA's Historical Hurricanes tool, there have only been six major Category 3 or stronger tropical cyclones recorded in the Arabian Sea (though accurate satellite records go back to just 1990.) The Arabian Sea doesn't get many tropical cyclones since it is small; furthermore, the Southwest Monsoon keeps the tropical cyclone season short, with a short season that lasts from May to early June before the monsoon arrives, then another short season in late October through November after the monsoon has departed. Strong Arabian Sea storms are rare due to high wind shear and copious dry air from the deserts of the Middle East, with just two Category 4 or 5 storms ever recorded--Gonu in 2007 and Phet in 2010. Both cyclones hit Oman after weakening below Category 4 strength. There are no recorded tropical storms to have hit Yemen, though the nation has been hit by two tropical depressions--Tropical Depression Keila in 2011, and Tropical Depression Three in 2008.

Forecast for Chapala
Recent satellite images show that Chapala degraded slightly in organization late Friday morning, and JTWC reduced the storm's estimated intensity to 150 mph winds as of 8 am EDT. However, the storm still has low wind shear, warm ocean waters near 30°C (86°F) that extend to great depth and favorable upper-level outflow. These conditions may allow the storm to intensify into a Category 5 storm by Saturday, as predicted by JTWC. Thereafter, weakening is likely as the storm encounters higher wind shear, lower oceanic heat content, and interaction with land. Chapala is likely to make landfall on Monday in a sparsely populated area in Yemen just west of the border with Oman. Hopefully, this will limit the impact on the people of Yemen, who are suffering food shortages due to war and drought. According to an October 30 article from Reuters, ten of Yemen's 22 governorates were assessed as being in an emergency food situation in June, one step below famine on a five-point scale. The assessment has not been updated since then, partly because experts have not managed to get sufficient access to survey the situation. About a third of the country's population, or 7.6 million people urgently require food aid, the The U.N. World Food Programme said (thanks go to wunderground member barbamz for alerting us to this article.)


Figure 3. The 5-day rainfall forecast from the 2 am EDT Friday, October 30, 2015 run of the HWRF model called for some truly stunning rainfall amounts in the parched desert region near the Yemen/Oman border: over two feet! Image credit: NOAA/EMC.


Figure 4. Average annual rainfall in Yemen. Image credit: CIA, via Perry-Castañeda Library Map Collection, University of Texas at Austin.

Catastrophic flooding possible with Chapala’s arrival
The latest forecasts take Chapala into the east coast of Yemen as a hurricane, and on into Saudi Arabia as a weakening tropical depression. Apart from any wind damage, this track will bring huge downpours to eastern Yemen and western Oman, where almost any amount of rainfall is an event worth noting. As shown in Figure 4, the annual average rainfall in Yemen is less than 2” along the immediate coast and less than 5” inland, except along higher terrain, where it can approach 10”. Local totals from Chapala could easily exceed 10”, with the latest run of the HWRF model predicting totals over 24" in some coastal mountainous regions. Southern Yemen was hard-hit by Tropical Depression Three of 2008, which came on the heels of heavy rains from another storm, and resulted in disastrous flooding in Yemen. According to EM-DAT, the international disaster database, that storm killed 90 people and did $400 million in damage, making it the second worst natural disaster in Yemen's history, behind a June 13, 1996 flood (thanks go to wunderground member TropicalAnalystwx13 for alerting us to this fact.) According to a report from the Global Facility for Disaster Reduction and Recovery, the 2008 cyclone dropped an average rainfall of 91 mm (3.58”) over an area of 2 million hectares (7722 square miles, or about the size of New Jersey). Losses totaled more than 6% of Yemen’s GDP, which would be the equivalent of a $1 trillion storm in the US. Although the 2008 Yemen cyclone arrived in the wake of several days of preceding rainfall, Chapala is a much stronger cyclone.

As Cyclone Gonu approached Oman back in 2007, guest blogger Margie Kieper provided this compelling description of how a storm like Chapala might affect this region.

"Imagine that you live directly on the Gulf, but in a place where it hardly ever rains, and where a hurricane has never hit, for at least a generation--for more than sixty years. Your community and many like yours are situated not only directly on the water, but near or in large dry riverbeds on the coastal plain, which is a narrow strip of sandy shoreline that is the dropoff for the three-thousand-foot mountain range behind it. Even many of the roads up into the mountains are in these dry riverbeds, which course through deep canyons as they rise into the heights. You don't have any idea what it might mean to experience winds of over 100 miles per hour, whipping up sand, and torrential rain against these mountains that can turn the riverbeds into conduits for dangerous flash floods. And you don't have any idea what storm surge is, and can't conceive of wind-driven high waves that could break against the shoreline and leave nothing behind.”

Air pollution blamed for an increase in strength of Arabian Sea tropical cyclones
Arabian Sea tropical cyclones during the pre-monsoon period in May and June have become stronger over the past 30 years owing to a reduction in vertical wind shear brought about by dimming of sunlight from air pollution particles primarily emitted in India, said Evan et al. in a 2011 paper published in the journal Nature. However, the study did not address how post-monsoon tropical cyclones in October and November, like Tropical Cyclone Chapala, might be impacted by air pollution.

Severe flash flooding in Austin/San Antonio area
A very dangerous situation was rapidly unfolding on Friday morning in and near the Hill Country of Texas, where surface low pressure was focusing repeated rounds of intense thunderstorms drawing on extremely high atmospheric moisture. At Austin's Bergstrom International Airport, where the tarmac was closed due to high water, 5.76" of rain was received in just one hour. Several CoCoRaHS stations have reported more than 10". Many roads are swamped, and high-water rescues are under way, with several counties under NWS Flash Flood Emergency status. We'll have more on this event in an upcoming post.

Jeff Masters and Bob Henson

Hurricane

South Africa Sets Earth's Hottest October Temperature on Record: 119°F

By: Jeff Masters , 2:33 PM GMT on October 29, 2015

Earth's hottest temperature ever recorded in the month of October occurred on Tuesday, October 27, 2015 in South Africa, when Vredendal hit a remarkable 48.4°C (119.1°F). According to weather records researcher Maximiliano Herrera, this is also the highest temperature ever observed at Vredendal and the third highest temperature in South African history. The new global October heat record was made possible by a "Berg wind"--a hot dry wind blowing down the Great Escarpment from the high central plateau to the coast. As the air descended it warmed via adiabatic compression, causing the record heat. These sorts of foehn winds are commonly responsible for all-time record temperatures; mainland Antarctica's all-time record high of 17.5°C (63.5°F), set on March 24, 2015, was due, in part, to a foehn wind (see wunderground weather historian Christopher C. Burt's blog post on this.)

According to Herrera, the previous world October heat record of 47.3°C was set at Campo Gallo, Argentina on 16 October 1936, and South Africa's highest reliable temperature for any month is 48.8°C (119.8°F), recorded at Vioosdrif in January 1993.


Figure 1. Five-minute resolution plot of the temperature at Vredendal, South Africa on October 27, 2015, when the station hit a remarkable 48.4°C (119.1°F)--an all-time record for the planet for the month of October. Image credit: South African Weather Service, with kudos to Gail Linnow.

Arabian Sea's Tropical Cyclone Chapala a threat to Yemen and Oman
In the Arabian Sea, Tropical Cyclone Chapala has spun up to hurricane strength, with top winds of 75 mph estimated at 8 am EDT Thursday by the Joint Typhoon Warning Center. Chapala is expected to take advantage of low wind shear, warm ocean waters near 30°C (86°F) and favorable upper-level outflow to intensify into a Category 4 storm by Sunday. Thereafter, weakening is likely as the storm encounters higher wind shear, lower oceanic heat content, and interaction with land. Chapala is likely to make landfall on Monday in a sparsely populated area near the border of Yemen and Oman.


Figure 2. Tropical Cyclone Chapala as seen by the VIIRS instrument at 08:30 UTC October 29, 2015. At the time, Chapala was intensifying from a tropical storm with 65 mph winds to a Category 1 storm with 75 mph winds. Image credit: NOAA/RAMMB.

Wunderblogger Steve Gregory has an a new Thursday afternoon post, Unseasonably Warm Weather Ahead – and More Rain. There's a super-cool 2-year+ animation of the change in sea surface height in the Pacific due to El Niño, check it out!

Jeff Masters

Heat Hurricane

Weather Underground Bought by IBM

By: Jeff Masters , 3:45 PM GMT on October 28, 2015

IBM announced today that it has entered into a definitive agreement to acquire The Weather Company’s B2B, mobile and cloud-based web properties, including WSI, weather.com, Weather Underground and The Weather Company brand. The TV segment – The Weather Channel – will not be acquired by IBM, but will license weather forecast data and analytics from IBM under a long-term contract.

There are no changes that have been announced for how Weather Underground will operate, and Bob Henson and I plan to ride the rapids to see where they lead. IBM brings some pretty remarkable technology resources to the table, so I expect that WU's creative development team will be able to take advantage of that and crank out some ground-breaking weather software.

For more information on the acquisition, see the IBM/Weather Company press release. The deal will likely become finalized in January.

Jeff Masters

Wunderground News

Weird Olaf Dies; Huge Tides Swamp SE U.S.; Indonesia Ties All-Time Heat Record

By: Jeff Masters and Bob Henson , 3:33 PM GMT on October 27, 2015

The weird and remarkable Northern Hemisphere tropical cyclone season of 2015 is on the wane, and we don't have any active systems anywhere on the planet to discuss today. On Tuesday morning, Tropical Storm Olaf met oblivion over the cool 25°C waters between Hawaii and California, ending a long run as a most unusual tropical cyclone. Back on October 19, Olaf set a record for becoming the most southerly major hurricane ever observed in the Eastern Pacific, at 9.9°N latitude. And on Monday night, Olaf performed another rare feat--crossing from the Central Pacific into Eastern Pacific. Moving from southwest to northeast, Olaf crossed the magic line of 140°W, which marks the boundary between the two ocean areas. The Central Pacific Hurricane Center (CPHC) in Hawaii stopped issuing advisories on the storm, and the National Hurricane Center (NHC) in Miami resumed issuing them. This was the second time Olaf had crossed 140°W--Olaf passed from the Eastern Pacific into the Central Pacific on October 20, causing a reverse hand-off of responsibility, from NHC to CPHC. Olaf is the only named storm ever to require a double hand-off of advisory issuing responsibility between the two hurricane centers. The only other storm to cross from the Central Pacific in the Eastern Pacific was an unnamed 1975 storm. Earlier this month, Tropical Storm Oho almost did so, becoming post-tropical just 50 miles before crossing 140°W from southwest to northeast. Since 1949, no late season (October or later) system has formed south of Hawaii and moved to the northeast; we know two storms this year that have done that, Oho and Olaf. This year's unusual activity in both the Eastern Pacific and Central Pacific has been due to unusually low wind shear and record-warm ocean temperatures caused by a strong El Niño event combined with the long-term global rise in temperatures underway.


Figure 1. MODIS image of Tropical Storm Olaf as seen from NASA's Aqua satellite on Monday afternoon, October 26, 2015, as the storm was about to cross 140°W from the Central Pacific into the Eastern Pacific. At the time, Olaf had top sustained winds of 60 mph. Image credit: NASA.

Earth's next tropical cyclone: an Arabian Sea storm?
In the Arabian Sea, Invest 94A is growing more organized, and is likely to become a named storm later this week as it heads westwards towards Oman and Yemen, according to recent runs of the GFS and European models.

The Atlantic and the Eastern Pacific are quiet, with none of our reliable models for predicting tropical cyclone genesis showing anything developing over the next five days. I'm not expecting any more named storms to form in the Atlantic this year, but I expect we'll get 1 - 2 more named storms in the Eastern Pacific and 2 - 4 more storms in the Northwest Pacific.


Figure 2. Predictions of the surface wind field of Invest 94A on Monday, November 2, 2015, from the 00Z Tuesday, October 27, 2015 runs of the GFS and European (ECMWF) models. Image constructed from our wundermap by TWC's Stu Ostro.

Indonesia ties all-time national heat record
Along with life-threatening amounts of smoke from agricultural burning during a very strong El Niño, Indonesians are dealing with extreme heat. On Tuesday, the airport station at Semarang, Indonesia, soared to a high of 39.5°C (103.1°F). This ties the national record for the hottest temperature ever observed in Indonesia, set in Cirebon Jatiwangi in 2006. These data come from international weather records researcher Maximiliano Herrera, one of the world's top climatologists, who maintains a comprehensive list of extreme temperature records for every nation in the world on his website. As documented in our October 21, 2015 post, there were fourteen nations or territories that had set or tied all-time heat records this year as of October 21. Indonesia brings that tally to sixteen, since Meteo France announced a new all-time high temperature record for French Guiana was set on October 22, 2015, when the mercury hit 37.8°C (100°F) at Saint Laurent du Moroni.

As El Niño-related drought intensifies its chokehold on the region, Indonesia’s pall of smoke and haze is only getting worse, and the effects are accumulating. Six Indonesian provinces have declared states of emergency, and since July more than 500,000 acute respiratory infections have been reported. Despite the health catastrophe, there is no national ban on agricultural fires. A spokesperson for Indonesia’s meteorological agency, Sutopo Puro Nugroho, said: “This is a crime against humanity of extraordinary proportions…But now is not the time to point fingers but to focus on how we can deal with this quickly.” As we noted earlier this month, the fires are Earth’s most expensive weather-related disaster of 2015. The Indonesian government now estimates that the total costs to the government are at least $30 billion (US dollars).


Figure 3. Motorists ride on a road as thick haze from forest fires shrouds the city in Palangkaraya, Central Borneo, Indonesia, on Tuesday, October 27, 2015. The haze has blanketed parts of western Indonesia for about two months and affected neighboring countries like Singapore, Malaysia and Thailand. Image credit: Associated Press.


Figure 4. An Indonesian soldier puts out a fire in Kampar in the Indonesian province of Riau on September 18, 2015. Image credit: Adek Berry/AFP/Getty Images.

Highest tides in decades sweep into Charleston, Savannah
A predicted high tide came in substantially stronger than expected this morning across much of the southeast U.S., especially along the South Carolina and Georgia coasts. Near Savannah, the Fort Pulaski station reported a tide of 10.43 feet above mean lower low water (MLLW). Even including hurricanes, this is the third highest tide at Fort Pulaski since records began in 1935, beaten only by 10.47’ on August 11, 1940 and 10.87’ on October 15, 1947 (thank to Nick Wiltgen at The Weather Channel for these records). At Charleston, the high tide of 8.68’ this morning was the highest in 26 years, beaten by 8.84’ (January 1, 1987), 10.27’ (August 11, 1940), and 12.56’ during Hurricane Hugo (September 21, 1989). Motorists in the Charleston area were asked to avoid traveling onto the peninsula this morning, with many roads blocked by accidents and/or high water.


Figure 5. Tidal records for October 24-27, 2015, at Fort Pulaski, Georgia, just southeast of Savannah. Image credit: NOAA Advanced Hydrologic Prediction Service.

It doesn’t take a hurricane to produce historically high tides. In this case, the high water is the result of strong coastal flow from the northeast (which pushed water onshore due to the Ekman transport effect) combined with a perigean spring tide. The latter occurs when the moon is at the closest point to Earth in its monthly orbit (perigean tide) and also happens to be either new or full (spring tide). Increasing sea levels as a result of human-produced climate change, combined with land subsidence in some areas, are making such events progressively worse. A NOAA primer on perigean spring tides notes: “In some instances, perigean spring tides have coincided with a shift in offshore ocean circulation patterns and large scale shifts in wind that have resulted in unexpected coastal flooding. It is expected that occurrences of minor 'nuisance flooding' at the times of perigean spring tides will increase even more as sea level rises relative to the land.” In September, NOAA predicted that atmospheric patterns related to El Niño will tend to drive more water into the coastline this autumn and winter, possibly leading to record amounts of nuisance flooding, especially along the mid-Atlantic coast.

Jeff Masters (tropical); Bob Henson (Indonesia, Southeast tides]



Hurricane Flood Heat Sea level rise

The Cataclysm That Wasn’t: Hurricane Patricia Largely Spares Mexico, Texas

By: Bob Henson , 1:42 PM GMT on October 26, 2015

Expectations of calamity were running high on Friday, October 23, as Hurricane Patricia neared the southwest coast of Mexico. Just a few hours earlier, top sustained winds in Patricia were 200 mph--the highest reliably-measured surface winds in any tropical cyclone on Earth--and its central surface pressure was 879 mb, the lowest sea-level pressure ever recorded in the Western Hemisphere. As Patricia stormed ashore, an automated station in Cuixmala, near the point of landfall, reported sustained winds of 185 mph, gusting to 211 mph (this report has not yet been evaluated or confirmed). Despite this ferocity, a number of factors lined up to minimize Patricia’s impact in Mexico, as we outlined on Saturday. These factors included the hurricane’s very small size; its landfall location, well away from the coastal population centers of Puerto Vallarta and Manzanillo; large-scale evacuations; the steep offshore topography of the landfall location, which reduced the potential storm surge; Patricia’s rapid motion, which reduced rainfall totals; and its speedy decay.


Figure 1. Aerial view of the Chamela community, Jalisco State, Mexico on October 24, 2015, after the passage of Hurricane Patricia. Patricia flattened dozens of homes on Mexico's Pacific coast, but authorities said Saturday the record-breaking hurricane largely spared the country as it weakened to a tropical depression. Photo credit: Mario Vazquez/AFP/Getty Images.


Figure 2. Residents stand outside their flooded house in Zoatlan, Nayarit state, some 150 km northwest of Guadalajara, Mexico, on Saturday, Oct. 24, 2015. Photo credit: Eduardo Verdugo/AP.


Figure 3. Patricia tracked just to the west of densely populated areas, thus greatly reducing its toll on southwestern Mexico. Image credit: Michael Lowry, The Weather Channel, @MichaelRLowry.

Two days after Patricia struck, it was increasingly apparent that the hurricane’s toll was far less than many had feared. As of late Sunday, eight deaths (three direct and five indirect) had been attributed to Patricia. Several feet of water flooded parts of Manzanillo, but Puerto Vallarta saw little significant impact. Destruction was widespread in a few small towns along Patricia’s immediate path, with hundreds of homes lost and landscapes ripped apart. According to storm surge expert Hal Needham, some of the worst surge damage occurred in the community of Barra de Navidad, just to the east of the grey circle showing maximum wind speeds in Figure 3. All in all, the total economic toll from Patricia in Mexico will likely be far below that caused by many weaker landfalling storms--perhaps less than $100 million US.


Patricia packed a lot of strength into its short life, maintaining at least Category 4 strength for a full 38% of its brief lifespan. Here are a few vital statistics:

Lifespan as tropical cyclone: 102 hrs
(became TD at 15Z 10/20/15, declared post-tropical at 21Z 10/24/15)

Lifespan at tropical storm strength: 84 hrs
(became TS at 3Z 10/21/15, downgraded to TD at 15Z 10/24/15)

Lifespan as hurricane: 54 hrs
(became Cat 1 at 9Z 10/22/15, downgraded from Cat 1 to TD at 15Z 10/24/15)

Lifespan as Cat 4/5 hurricane: 39 hrs
(became Cat 4 at 18Z 10/22/15, downgraded to Cat 1 at 09Z 10/24/15)



Figure 4. Wind speed in a hurricane is strongly correlated with the central pressure, as shown in this graphic for all Northeast Pacific hurricanes from 1954 through 2013. Patricia bore out this relationship as it intensified (white dashed line) to peak winds of nearly 175 knots and a minimum central pressure of 879 mb (yellow star). Image credit: Patrick Marsh, @pmarshwx.

Patricia’s remnants in Texas: wet but not too wild
Patricia’s impact on Texas also fell short of what could have transpired. As the hurricane’s remnants passed over the Texas coast on Saturday night and Sunday, they helped spin up a nontropical coastal low, as expected. But the heaviest rains stayed offshore, as the low was hustled along by a large upper-level trough moving across the state. Rainfall amounts averaged 5” to 10” from the central coast across the Houston area, resulting in widespread but non-catastrophic flooding. The heavy rains translated east into Lousiana and Mississippi on Sunday, as did flash flood watches and warnings. Baton Rouge notched 8.60” and the New Orleans airport picked up 8.67”, both setting monthly records for any single date in October. Even larger amounts of rain fell from Thursday through Saturday across central Texas, as the upper-level trough and an associated surface front interacted with rich Gulf moisture ahead of Patricia’s remnants (see radar loop embedded below). The area near Corsicana was hardest-hit, with the town of Powell receiving a three-day total of 20.15.” The multiday event pushed the Dallas-Fort Worth area into seventh place for its wettest year on record. With 46.64” up through Saturday, the DFW metro area is within striking distance of the record 53.54” observed in 1991.


Figure 5. A dropsonde launched by this NOAA crew on Friday, October 23, 2015, measured the lowest pressure ever recorded in a Western Hemisphere hurricane: 879 millibars. Left to right: (top row) Joe Sapp, Mike Holmes, Joseph Klippel, Lonnie Kregelka, Jim Warnecke, Tim Gallagher, Chris Lalonde, Bill Olney, Dana Naeher, Bobby Peek; (bottom row) Pat Didier, Scott Price and Adam Abitbol. Photo credit: Courtesy Joseph Klippel

A reconnaissance flight for the ages
The Hurricane Hunters who fly into storm after storm for NOAA and the U.S. Air Force may carry out hundreds of flights in a career, many of which garner little notice. But one foray of the NOAA P-3 aircraft dubbed ”Miss Piggy” will go down in history. During a single 10.5-hour flight on Friday, October 23, the NOAA team flew from Harlingen, TX, across Mexico; made two passes through the heart of Hurricane Patricia; and then flew back to their home base of MacDill AFB in Tampa, FL. One of the dropsondes the team launched into Patricia during that Friday flight recorded the 879-millibar central pressure that now stands as a Western Hemisphere record. The embedded video below gives a taste of what the crew encountered a day earlier, on Thursday, as they flew through the eyewall of Patricia while the hurricane was intensifying rapidly.

Hal Needham has a blog post this morning with photos and analysis of surge damage in Mexico related to Patricia's landfall. WU contributor Steve Gregory also has a new post, weighing in on another Texas rain event possible this coming weekend, followed by mild weather for much of the nation to kick off November.

Bob Henson

This video of our 1st eye wall penetration into Hurricane Patrica. The 1st two minutes is the approach and actual eye wall penetration, the next 2 minutes is in the actual eye of the storm and the last minute is our entry into the other side of the eye wall.

Posted by Joseph Diane Klippel on Thursday, October 22, 2015



Texas radar loop October 23-24, 2015

Inflow of moist unstable air from the southeast interacting with a front to produce training thunderstorms with flash flooding, then outflow racing to the southeast. Image credit: College of DuPage Meteorology

Posted by Stu Ostro on Saturday, October 24, 2015


Hurricane

Patricia’s Remnants to Fuel Dangerous Rains in Texas

By: Jeff Masters and Bob Henson , 6:09 PM GMT on October 24, 2015

After growing extraordinarily quickly to Category 5 strength, and striking the Mexican coast less than a day later, Tropical Depression Patricia is rapidly dissipating--leading to one of the most abbreviated life cycles on record for any Category 5 tropical cyclone. At 11 am EDT Wednesday, Patricia was a minimal tropical storm, with 40 mph winds. A mere 36 hours later, Patricia packed winds of 160 mph, eventually reaching 200 mph--the highest reliably measured surface winds in any tropical cyclone on Earth. After 36 more hours (at 11 am EDT Saturday) Patricia’s sustained winds were back down to 35 mph. As with all tropical cyclones, Patricia’s landfall was its downfall: the hurricane slammed into rugged coastal terrain while accelerating northeastward, which quickly shredded its low-level circulation. At 11 am EDT Saturday, Patricia’s low-level center was located in central Mexico, about 100 miles northeast of Zacatecas. Unimpeded by the mountainous terrain, Patricia’s upper-level circulation is racing more quickly to the northeast, on its way to help generate a large area of torrential rain tonight across southern Texas.


Figure 1. MODIS image of Hurricane Patricia as seen from NASA's Aqua satellite just before landfall at 4:35 pm EDT Friday, October 23, 2015. At the time, Patricia was a Category 5 storm with 190 mph winds. Image credit: NASA.


Figure 2. Rainfall from Hurricane Patricia for the 24 hours ending at 8 am CDT October 24, 2015. The maximum rainfall was 11.43" (290.2 mm) in Nevado de Colima, marked by a triangle. Note: 1" = 25.4 mm. Image credit: Conagua.

Why didn't Patricia cause more death and destruction?
After a landfall by a Category 5 storm that was the strongest landfalling hurricane ever recorded in the Eastern Pacific, many were expecting today to hear reports of huge swaths of mind-boggling devastation in Mexico. While it is too soon to be confident that major loss of life was avoided until we hear from the hardest-hit areas, there is reason to be optimistic that the death toll from Patricia will be low. The storm hit a relatively sparsely populated area, missing the cities of Puerto Vallarta (population 380,000) to its left and Manzanillo (population 100,000) to its right. The region of coast most affected by the storm surge did not have a large area of shallow water offshore conducive for piling up a huge storm surge. Patricia's Category 5 winds were confined to a relatively narrow swath about fifteen miles in diameter, and this swath missed major cities. While Patricia did dump torrential rains along its path, the storm was moving fast enough at landfall--about 20 mph--that these heavy rains did not stay in place long enough to generate the kinds of devastating floods we've seen in the past from Mexican hurricanes.


Figure 3. Soldiers evacuate residents to a shelter in Zoatlan, Nayarit state, about 150 km northwest of Guadalajara, Mexico, on Saturday, October 24, 2015, as Hurricane Patricia brought heavy rains to the region. Image credit:  Eduardo Verdugo/AP.


Credit also needs to be given to Mexican civil defense efforts, which have historically been among the best in the world at getting people out of harm's way from approaching hurricanes. In 2005, Hurricane Emily made landfall on the Mexican coast near Cozumel Island as a Category 4 storm with 135 mph winds and a storm surge of up to 15 feet. Emily went on to cross the Gulf of Mexico and slam ashore on the Mexican coast south of Brownsville, Texas, as a Category 3 hurricane. Only three people died in Mexico from Emily's double strike on the country as a major hurricane--two of the deaths from a helicopter that crashed while evacuating offshore oil rigs. In addition, Mexico suffered only eight deaths from Hurricane Wilma's $7.5 billion four-day pounding in 2005. Wilma started out as a Category 4 hurricane with 150 mph winds when it hit Cozumel Island, and gradually weakened to a Category 2 hurricane as it plowed north over Cancun and eventually into the Gulf of Mexico. Mexico's feat of surviving two strikes from a Category 4 hurricane, plus a Category 3 strike to populated areas, with only eleven deaths, is a civil defense success unparalleled in hurricane history.

Life-threatening floods possible through Sunday in central Texas
While not as dramatic as an approaching Category 5 hurricane, a mammoth heavy-rain episode this weekend in Texas has real potential for harm and damage. The locations at greater risk include from the Hill Country west of Austin and San Antonio, extending through these major metro areas to the Houston area. Rainfall amounts in some areas have already exceeded the top amounts produced by Hurricane Patricia’s landfall in Mexico, and more is on the way.


Figure 4. Rainfall amounts (in inches) observed in the 24 hours from 12Z Friday, October 23, through Saturday, October 24. Image credit: NOAA Advanced Hydrologic Prediction Service.


Figure 5. Rainfall amounts predicted for the 3-day period from 12Z (8:00 am EDT) Saturday, October 24, through Tuesday, October 27. Some local amounts will be significantly higher than the larger-scale totals shown here. Image credit: NOAA/NWS Weather Prediction Center.


Several ingredients are converging across the heart of Texas to produce an event that will be unusually intense and prolonged even for this flood-familiar region. Heavy rains have been lumbering across the northwestern two-thirds of the state since Thursday, the result of a large upper-level trough over the Rockies coupled with strong, moist southerly flow. Showers and thunderstorms intensified across central TX on Friday night along an east-west surface boundary just south of the Dallas-Fort Worth area. From Thursday morning through noon CDT Saturday, a total of 19.07” of rain fell at Corsicana, where Interstate 45 was closed in both directions at midday Saturday.

Coastal low could produce noteworthy flooding on Texas coast
With the main upper trough lifting out, a stronger cold front will plow southeast tonight, colliding with the upper-level remnants of Patricia over central and southeast Texas. A low-level jet will likely develop, importing even more moisture into the area. The upper-level energy from Patricia will help focus a new surface low near the middle Texas coast tonight that will translate slowly northeast near Houston on Sunday and into Louisiana on Monday. Models suggest that winds along the Texas coast could approach tropical storm strength near this surface low, and it may exhibit some subtropical characteristics, but the low will be driven mainly by nontropical processes and it is unlikely to be classified or named by the National Hurricane Center. The prolonged, strengthening southeast flow ahead of the low will lead to some coastal and tidal flooding, especially in the Houston-Galveston area.


Figure 6. WunderMap depiction of surface winds (in knots; multiply by 1.15 for mph) predicted by the 06Z Saturday run of the GFS model for 18Z (1:00 pm CDT) Sunday, October 25, 2015.


Storm surge expert Hal Needham, who is in the area this weekend for a conference, notes that water levels at Galveston have been running more than a foot above normal for several days, and a three-foot surge is possible on Sunday as the coastal low strengthens. In a blog post on Saturday morning, he warned: “Although a 3-foot (0.91 m) storm surge is not phenomenal for Galveston, a prolonged 2-3 foot (0.6-0.91 m) surge could have dire impacts if accompanied by 10 or more inches of rain. Most drainage around the Houston- Galveston area is gravity-fed, meaning the drainage depends on a noticeable slope between the ground and the water body into which the rainwater is discharged, like a bayou, channel, Galveston Bay or the Gulf of Mexico. If Galveston Bay is elevated 2-3 ft (0.6-0.91 m) above normal, the slope between land and water is reduced considerably, making rainfall drainage less efficient. This becomes a major concern when looking at the extraordinary rainfall in the forecast.” Needham (@Hal_Needham on Twitter) will be in the Houston-Galveston area through the weekend and invites readers to send him questions, comments, photos, or videos related to this event.

Record atmospheric moisture at hand
Atmospheric moisture is already at record levels for late October across far south Texas (see Figure 7), and rainfall rates as high as 4.5”/hour have already observed. With the factors above converging after dark on Saturday, extremely intense rains can be expected over a large part of southern Texas from Saturday night into Sunday. People in flood-prone areas such as the Hill Country will need to be especially vigilant. Urban flooding is a particular concern tonight in Austin and San Antonio and on Sunday in Houston, where it could be compounded by the surge issues mentioned above. Isolated tornadoes are also possible on Saturday afternoon and evening, especially near the Texas coast, as highlighted by the Storm Prediction Center in its latest convective outlook.

Jeff Masters and Bob Henson


Figure 7. Precipitable water (water vapor) in the atmosphere above Brownsville, TX, in soundings from all radiosondes launched from Brownsville, TX, from Jan. 1, 1948, through Oct. 26, 2014. The spiky red line shows the record-high values observed on each date. Depicted with the starburst at upper right is the record value of 2.62” measured at 12Z on Saturday morning, October 24, 2015. This is the highest value ever observed in Brownsville on any date between September 16 and June 19. At Corpus Christi, TX (not shown), Saturday morning’s value of 2.52” is a record for any date between October 20 and June 20. Image credit: NOAA Storm Prediction Center.

Hurricane Flood

Category 5 Hurricane Patricia Hitting Mexico's Pacific Coast

By: Jeff Masters , 10:13 PM GMT on October 23, 2015

Incredibly strong Hurricane Patricia is barreling ashore on the Southwest coast of Mexico near La Manzanilla as a Category 5 storm. At 5 pm EDT Friday, NHC put Patricia's intensity at 190 mph winds. Early on Friday morning, Patricia reached a remarkable intensity of 200 mph sustained winds, which the storm maintained for 12 hours. These are the highest reliably-measured surface winds on record for a tropical cyclone, anywhere on the Earth. At 2:30 pm Friday afternoon, October 23, 2015, a NOAA hurricane hunter aircraft measured a central pressure of 879 mb--the lowest pressure ever measured in a hurricane in the Western Hemisphere. The previous strongest Eastern Pacific hurricane was Hurricane Linda of 1997, with a pressure of 902 mb (estimated from satellite imagery), and the strongest Atlantic hurricane on record was Hurricane Wilma of 2005, with 882 mb. Patricia does not beat the record-lowest pressure in the Western Pacific, though, which is held by Super Typhoon Tip of 1979: 870 mb.


Figure 1. MODIS image of Hurricane Patricia as seen from NASA's Aqua satellite on Friday, October 23, 2015. At the time, Patricia was a Category 5 storm with 200 mph winds. Image credit: NASA.


Figure 2. Hurricane Patricia as seen from the International Space Station on Friday afternoon, October 23, 2015. Image credit: Commander Scott Kelly.


Figure 3. Wind (black) and surface pressure (red) from the afternoon NOAA hurricane hunter flight on October 23, 2015 into Hurricane Patricia, off the Pacific coast of Mexico. The aircraft measured peak winds at their flight level of 10,000 feet of up to 145 knots (165 mph). The winds showed a double maximum in both sides of the eyewall as the plane flew crossed the calm eye, indicating that an eyewall replacement cycle was likely underway. The eye was a tiny 6 miles in diameter at this time. Image credit: Levi Cowan, tropicaltidbits.com.

Patricia weakening at landfall
Late-afternoon data from a NOAA hurricane hunter aircraft in Patricia indicates that the hurricane is forming concentric eyewalls, presaging an eyewall replacement cycle, where the inner eyewall collapses and is replaced by an outer eyewall that forms out of a spiral band. This process typically weakens the peak winds of the hurricane by up to 20 mph, but spreads out the highest winds of the storm over a larger area. This process typically reduces the wind damage from a storm, but makes a larger storm surge, leading to more storm surge damage.


Figure 4. Radar image of Hurricane Patricia as seen from NOAA Hurricane Hunter aircraft N43RF at 1:23 pm EDT October 23, 2015. Image credit: NOAA Hurricane Hunters Facebook page.

Patricia the fastest-intensifying Western Hemisphere hurricane on record
Patricia's central pressure dropped an astonishing 100 mb in 24 hours, making it the fastest-intensifying hurricane ever observed in the Western Hemisphere. Patricia's pressure at 5 am EDT Thursday, October 22, 2015 was 980 mb, and was 880 mb at 5 am EDT Friday. The previous record was a drop of 97 mb in 24 hours for Hurricane Wilma of 2005 (between 1200 UTC 18 October - 1200 UTC 19 October), according to the official NHC report for the storm. Patricia's intensification rate was very close to the WMO-recognized world record for fasting-intensifying tropical cyclone: 100 millibars in just under 24 hours by Super Typhoon Forrest in the Northwest Pacific in 1983.

Patricia is estimated to have intensified 85 knots (100 mph) in 24 hours, from a tropical storm to a Category 5 hurricane. In the Eastern Pacific, Hurricane Linda of 1997 is the only storm on record to have intensified at this rate. The Atlantic's record holder for largest wind increase in 24 hours is held by Hurricane Wilma of 2005, which intensified from a 60-knot tropical storm to a 150-knot Category 5 hurricane--an increase of 90 knots (105 mph). Air Force reconnaissance observations indicated that the eye of Wilma contracted to a diameter of 2 n mi during this time; this is the smallest eye known to National Hurricane Center (NHC) staff. Patricia's eye diameter was 8 miles at it's peak strength.


Figure 5. Maximum Potential Hurricane Intensity (MPHI) for the Eastern Pacific on October 23, 2015, calculated according to a method developed by Dr. Kerry Emanuel. The MPHI for the waters traversed by Hurricane Patricia was less than 880 mb. Few storms ever approach their maximum theoretical intensity, but Hurricane Patricia did--reaching 879 mb at 2 pm EDT October 23, according to measurements from the Hurricane Hunters. The Maximum Potential Hurricane Intensity is maximized as the sea surface temperature rises and as the atmosphere grows more unstable (cold, dry air aloft combined with warm, moist air near the surface.) Image credit: COLA/IGES.

Patricia the third strongest tropical cyclone in history (by wind)
Patricia's 200 mph sustained winds make it the 3rd strongest tropical cyclone in world history (by 1-minute averaged wind speed.) Officially, here are the strongest tropical cyclones in world history, according to the Joint Typhoon Warning Center and the National Hurricane Center (using 1-minute averaged sustained winds):

Super Typhoon Nancy (1961), 215 mph winds, 882 mb. Made landfall as a Cat 2 in Japan, killing 191 people.
Super Typhoon Violet (1961), 205 mph winds, 886 mb pressure. Made landfall in Japan as a tropical storm, killing 2 people.
Super Typhoon Ida (1958), 200 mph winds, 877 mb pressure. Made landfall as a Cat 1 in Japan, killing 1269 people.
Super Typhoon Haiyan (2013), 195 mph winds, 895 mb pressure. Made landfall in the Philippines with 190 mph winds.
Super Typhoon Kit (1966), 195 mph winds, 880 mb. Did not make landfall.
Super Typhoon Sally (1964), 195 mph winds, 895 mb. Made landfall as a Cat 4 in the Philippines.

However, it is now recognized (Black 1992) that the maximum sustained winds estimated for typhoons during the 1940s to 1960s were too strong. The strongest reliably measured tropical cyclones were both 10 mph weaker than Patricia, with 190 mph winds—the Western Pacific's Super Typhoon Tip of 1979, and the Atlantic's Hurricane Allen of 1980. Both storms had a hurricane hunter aircraft inside of them to measure their top winds. Haiyan's winds were estimated using only satellite images, making its intensity estimate of lower confidence.

Dr. Hugh Willoughby, former head of NOAA's Hurricane Research Division, had this to say about the winds measured in Super Typhoon Nancy and the other high-end typhoons from this list from the 1960s:

"I would not take the winds seriously because reconnaissance meteorologists estimated them visually. A decade later when I flew with the VW-1 hurricane hunters, we had the same Doppler system used to measure the winds of Typhoon Nancy. It tracked the aircraft motion relative to the (possibly moving) sea surface. It couldn't get a coherent signal in high winds because the beam reflected from both the actual surface (whatever that is) and blowing spray. Visual estimates are dubious because the surface (under the eyewall!) is hard to see unless you are flying below cloud base (200-300 m) and also because appreciably above 115 mph, it's completely white with blowing spray. We used to think that we could estimate stronger winds from the decreasing coverage of slightly greenish patches where the spray was thinner. I now think that we were kidding ourselves. In those days the distinctions among wind gust, sustained one-minute winds, etc., were less well defined than they are now. So we may never know the 1960s reconnaissance data really means!"

Forecast for Patricia: Mexico at dire risk
The coast of Southwest Mexico is at risk of tremendous damage from wind, storm surge, and flooding rains. The right front quadrant of the storm, near the town of La Manzanilla, can expect gigantic waves atop a devastating storm surge. In a Friday afternoon blog post, storm surge expect Dr. Hal Needham says he expects a storm surge of 16.5 ft (5 m), which will be accompanied by large, destructive waves. This would be the largest storm surge in the modern history of Western Mexico. Fortunately, hurricane-force winds are likely to miss the resort town of Puerto Vallarta, which lies on the weaker left side of the hurricane. In their 5 pm EDT Friday WInd Probability Forecast, NHC gave Puerto Vallarta a 19% chance of seeing hurricane-force winds of 74+ mph. However, the town of Manzanillo (population 100,000), on the right-front quadrant of Patricia, had a 49% chance of hurricane-force winds.

After landfall, Patricia will slam into very rugged terrain, triggering torrential rains with the risk of severe flooding and mudslides. The mountainous trek will shred Patricia’s low-level circulation quickly, but the hurricane’s upper-level circulation will proceed quickly northeastward, arriving near South Texas by Sunday. Models suggest that a nontropical or hybrid low-pressure center may develop near the upper-level center at that point. Patricia’s presence will exacerbate a multi-day rain/flood episode already under way across Texas, with widespread 4” - 8” rainfall amounts across the eastern half of the state expected between now and Monday. Localized totals well over a foot are quite possible.

iCyclone storm chasers in the path of Patricia
Storm chaser Josh Morgerman, who intercepted Super Typhoon Haiyan at landfall in Tacloban in the Philippines, is aiming to be in the path of Hurricane Patricia's eye at landfall in Mexico. From the iCyclone Facebook page: "12:30 pm Friday (Jalisco): Erik and I noticed on satellite loops this morning that Hurricane PATRICIA's eye took a sharp hook to the right. We waited a little, then realized it was more than a wobble--so we loaded up the car and raced down Highway 200. Now we're in La Manzanilla, which we think could be very close to the cyclone's landfall point. But more adjustments might be needed. It's calm but raining very hard. La Manzanilla is an eerie ghost town. Everything is boarded up and shuttered. Still can't believe what's just offshore. You'd have to be a Cat-5 idiot not to be scared of it. Despite years and years of chase experience, I'm just in awe of this one." Live reports from the iCyclone team will be airing on The Weather Channel all day.

Other Links:
Manzanillo beach cam
Puerto Vallarta webcam
‪International Space Station Footage of Hurricane Patricia‬


Video 1. GOES-13 satellite loop of Hurricane Patricia.

Jeff Masters

Hurricane

Stunning, Historic, Mind-Boggling, and Catastrophic: Hurricane Patricia Hits 200 mph

By: Jeff Masters and Bob Henson , 5:04 PM GMT on October 23, 2015

Stunning, historic, mind-boggling, and catastrophic: that sums up Hurricane Patricia, which intensified to an incredible-strength Category 5 storm with 200 mph winds overnight. At 2:46 am EDT October 23, 2015 an Air Force hurricane hunter aircraft measured a central pressure of 880 mb in Patricia, making it the most intense hurricane ever observed in the Western Hemisphere. The aircraft measured surface winds of 200 mph, which are the highest reliably-measured surface winds on record for a tropical cyclone, anywhere on the Earth. The previous strongest Eastern Pacific hurricane was Hurricane Linda of 1997, with a pressure of 902 mb (estimated from satellite imagery.) The strongest Atlantic hurricane on record was Hurricane Wilma of 2005, with an 882 mb central pressure. Patricia does not beat the record-lowest pressure in the Western Pacific, though, which is held by Super Typhoon Tip of 1979: 870 mb.


Figure 1. GOES-East satellite image of Hurricane Patricia at 10:45 am EDT October 23, 2015. Image credit: NOAA Viz Lab.


Figure 2. Wind barbs from the early-morning October 23, 2015 Air Force hurricane hunter mission into Hurricane Patricia, off the Pacific coast of Mexico. The aircraft measured winds of Category 5 strength (dark pink colors) at their flight level of 10,000 feet across a 20-mile diameter region. Winds at the surface as measured by a dropsonde were 9% lower compared to winds measured at flight level, so we likely there was a region at least 15 miles in diameter of Category 5 winds at the surface. Image credit: Levi Cowan, tropicaltidbits.com.

Patricia the fastest-intensifying Western Hemisphere hurricane on record
Patricia's central pressure dropped an astonishing 100 mb in 24 hours, making it the fastest-intensifying hurricane ever observed in the Western Hemisphere. Patricia's pressure at 5 am EDT Thursday, October 22, 2015 was 980 mb, and was 880 mb at 5 am EDT Friday. The previous record was a drop of 97 mb in 24 hours for Hurricane Wilma of 2005 (between 1200 UTC 18 October - 1200 UTC 19 October), according to the official NHC report for the storm. Patricia's intensification rate was very close to the WMO-recognized world record for fasting-intensifying tropical cyclone: 100 millibars in just under 24 hours by Super Typhoon Forrest in the Northwest Pacific in 1983.

Patricia is estimated to have intensified 85 knots (100 mph) in 24 hours, from a tropical storm to a Category 5 hurricane. In the Eastern Pacific, Hurricane Linda of 1997 is the only storm on record to have intensified at this rate. The Atlantic's record holder for largest wind increase in 24 hours is held by Hurricane Wilma of 2005, which intensified from a 60-knot tropical storm to a 150-knot Category 5 hurricane--an increase of 90 knots (105 mph). Air Force reconnaissance observations indicated that the eye of Wilma contracted to a diameter of 2 n mi during this time; this is the smallest eye known to National Hurricane Center (NHC) staff. Patricia's eye diameter was 8 miles at it's peak strength.




Figure 4. Infrared VIIRS images of Hurricane Patricia (top) and Super Typhoon Haiyan (bottom) near peak strength, showing the similarity in satellite presentations of the two storms. Image credit: Dan Lindsey, NOAA and NOAA/RAMMB.

Patricia the third strongest tropical cyclone in history (by wind)
Patricia's 200 mph sustained winds make it the 3rd strongest tropical cyclone in world history (by 1-minute averaged wind speed.) Officially, here are the strongest tropical cyclones in world history, according to the Joint Typhoon Warning Center and the National Hurricane Center (using 1-minute averaged sustained winds):

Super Typhoon Nancy (1961), 215 mph winds, 882 mb. Made landfall as a Cat 2 in Japan, killing 191 people.
Super Typhoon Violet (1961), 205 mph winds, 886 mb pressure. Made landfall in Japan as a tropical storm, killing 2 people.
Super Typhoon Ida (1958), 200 mph winds, 877 mb pressure. Made landfall as a Cat 1 in Japan, killing 1269 people.
Super Typhoon Haiyan (2013), 195 mph winds, 895 mb pressure. Made landfall in the Philippines with 190 mph winds.
Super Typhoon Kit (1966), 195 mph winds, 880 mb. Did not make landfall.
Super Typhoon Sally (1964), 195 mph winds, 895 mb. Made landfall as a Cat 4 in the Philippines.

However, it is now recognized (Black 1992) that the maximum sustained winds estimated for typhoons during the 1940s to 1960s were too strong. The strongest reliably measured tropical cyclones were both 10 mph weaker than Patricia, with 190 mph winds—the Western Pacific's Super Typhoon Tip of 1979, and the Atlantic's Hurricane Allen of 1980. Both storms had a hurricane hunter aircraft inside of them to measure their top winds. Haiyan's winds were estimated using only satellite images, making its intensity estimate of lower confidence.

Dr. Hugh Willoughby, former head of NOAA's Hurricane Research Division, had this to say about the winds measured in Super Typhoon Nancy and the other high-end typhoons from this list from the 1960s:

"I would not take the winds seriously because reconnaissance meteorologists estimated them visually. A decade later when I flew with the VW-1 hurricane hunters, we had the same Doppler system used to measure the winds of Typhoon Nancy. It tracked the aircraft motion relative to the (possibly moving) sea surface. It couldn't get a coherent signal in high winds because the beam reflected from both the actual surface (whatever that is) and blowing spray. Visual estimates are dubious because the surface (under the eyewall!) is hard to see unless you are flying below cloud base (200-300 m) and also because appreciably above 115 mph, it's completely white with blowing spray. We used to think that we could estimate stronger winds from the decreasing coverage of slightly greenish patches where the spray was thinner. I now think that we were kidding ourselves. In those days the distinctions among wind gust, sustained one-minute winds, etc., were less well defined than they are now. So we may never know the 1960s reconnaissance data really means!"

At the same time, we should keep in mind that not all hurricanes are sampled while at peak strength. Satellite methods of estimating intensity, such as the Dvorak technique, cannot capture the most extreme peak winds and central pressures found in storms such as Patricia and Wilma. It is possible that previous hurricanes, such as the 1935 Labor Day hurricane that devastated the Florida Keys, had intensification rates and peak winds on par with Patricia. The bottom line is that Patricia is at the very highest end of what we can expect in terms of a small, extremely intense hurricane.

The size of a hurricane also shapes its destructive power. Although Sandy was never a Category 4 or 5 hurricane, its longevity and size enabled it to move as much water in the form of waves and surge as Category 5 Katrina. We are lucky that Patricia is no larger than it is--although this is cold comfort for those who will be directly affected.



Figure 4. MODIS image of Hurricane Patricia as seen from NASA's Terra satellite on Thursday, October 22, 2015. At the time, Patricia was a Category 4 storm with 130 mph winds. Image credit: NASA.

Forecast for Patricia: Manzanillo at dire risk
Satellite loops early Friday afternoon showed that Patricia’s cloud tops had begun to warm, indicating weakening, and with wind shear now a moderate 10 - 20 knots and interaction with land beginning to occur, Patricia will likely weaken to 155 - 175 mph winds by landfall. The storm's expected turn toward the northeast has begun, and the storm is beginning to accelerate toward the coast of the Mexican state of Colima.

At particular risk is the city of Manzanillo, a regional center that straddles the back of a bay spanning several miles. On its current track, and with some acceleration in progress, it appears that Patricia could make landfall sometime between 5:00 and 9:00 pm EDT (4:00 - 8:00 local time, CDT] just to the northwest of Manzanillo--a trajectory that raises the odds of a catastrophic storm surge in or near Manzanillo. Patricia’s strongest winds are confined to a relatively small area, with hurricane-force winds only spanning a range of 30 miles from Patricia’s center. Category 5 winds of 156+ mph cover an area 15 miles across. Wherever those winds are focused, we can expect gigantic waves atop a devastating surge. An unnamed 1959 hurricane--the deadliest in Northeast Pacific history, with an estimated 1800 direct and indirect fatalities--struck near Manzanillo on October 27 (see embedded YouTube newsreel footage below). In a Friday afternoon blog post, storm surge expect Dr. Hal Needham says he expects a storm surge of 16.5 ft (5 m), which will be accompanied by large, destructive waves. This would be the largest storm surge in the modern history of Western Mexico.

After landfall, Patricia will slam into very rugged terrain, triggering torrential rains with the risk of severe flooding and mudslides. The mountainous trek will shred Patricia’s low-level circulation quickly, but the hurricane’s upper-level circulation will proceed quickly northeastward, arriving near South Texas by Sunday. Models suggest that a nontropical or hybrid low-pressure center may develop near the upper-level center at that point. Patricia’s presence will exacerbate a multi-day rain/flood episode already under way across Texas, with widespread 4” - 8” rainfall amounts across the eastern half of the state expected between now and Monday. Localized totals well over a foot are quite possible.

iCyclone storm chasers in the path of Patricia
Storm chaser Josh Morgerman, who intercepted Super Typhoon Haiyan at landfall in Tacloban in the Philippines, is aiming to be in the path of Hurricane Patricia's eye at landfall in Mexico. From the iCyclone Facebook page: "7:30 am Friday (Jalisco): Erik and I are staring down the barrel of a gun. Incredible Hurricane PATRICIA-- possibly the most intense hurricane in recorded history-- is just offshore with winds of 175 knots (200 mph). The NHC forecast track takes the center right over our current location. To say we have conflicted feelings is an understatement. We want to see history unfold. We also don't want to die. Main task-- as soon as we have daylight-- is to find a really good building in Perula or nearby La Fortuna. We're thinking closer to the main road-- away from the water."

Other Links:
Manzanillo beach cam
Puerto Vallarta webcam

We'll have a new update this afternoon, after a NOAA hurricane hunter aircraft arrives in the storm.


Video 1. Newsreel footage of the aftermath of the unnamed 1959 hurricane that devastated Manzanillo, Mexico.

Jeff Masters and Bob Henson

Hurricane

Hurricane Patricia Hits Category 5 En Route to Mexican Coast

By: Bob Henson , 4:28 AM GMT on October 23, 2015

History is being made tonight in the Northeast Pacific as Hurricane Patricia churns about 200 miles off the coast of Mexico, south-southwest of Manzanillo. With its 11 pm EDT Thursday advisory, the National Hurricane Center upgraded Patricia to Category 5, with top sustained winds of 160 mph and a central pressure of 924 millibars. Hurricane warnings are now in effect for the coast from San Blas to Punta San Telmo, including Puerto Vallarta and Manzanillo, with a hurricane watch and tropical storm warning eastward to Lazaro Cardenas. Update: Late Thursday night, an Air Force Hurricane Hunter flight captured some of the most extreme observations ever recorded in 70 years of reconnaissance activity. Based on flight-level winds of 179 knots (206 mph), NHC upgraded Patricia's strength at 12:30 am EDT Friday to 185 mph. The estimated surface pressure of 892 mb is the lowest on record for the Northeast Pacific, and it ranks #3 for the entire Western Hemisphere behind only Wilma (882 mb, on October 19, 2005) and Gilbert (888 mb, on September 13, 1988). A surface reading of 892 mb was recorded at Key West during the Labor Day hurricane (September 2, 1935).


Figure 1. Satellite image of Hurricane Patricia at 0347Z Friday, October 23, 2015 (11:47 pm EDT Thursday).


Figure 2. Visible satellite image of Hurricane Patricia close to nightfall, at 2345Z (7:45 pm EDT) Thursday, October 22. 2015. Image credit: NOAA and CIMMS/SSEC/University of Wisconsin.


Figure 3. Enhanced infrared satellite image of Hurricane Patricia from near sunset on Thursday, October 22. 2015. Image credit: CIMMS/SSEC/University of Wisconsin, courtesy Stu Ostro.

Satellite imagery of Patricia late Thursday was stunning, as the hurricane carved out a very symmetric core of intensifying convection (showers and thunderstorms) with a small eye at its center. Cloud-top temperatures within the convection are as cold as -130°F, a sign of extremely powerful updrafts. Patricia’s rate of strengthening since Wednesday has been truly remarkable. In a mere 36 hours, Patricia’s official NHC rating went from minimal tropical storm (40 mph) to Category 5 hurricane--among the most rapid intensification rates one might expect in a hurricane anywhere. NHC’s advisory on Thursday night placed Patricia in the elite group of 15 Northeast Pacific hurricanes that have reached Category 5 strength since 1959. One of those--an unnamed storm that struck near Manzanillo in 1959--is expected to be downgraded to Category 4 later this year after a reanalysis of data is confirmed. It remains the deadliest Northeast Pacific hurricane to date, resulting in an estimated 1800 direct and indirect fatalities.


Figure 4. The eye of Hurricane Patricia as seen by the navigator on NOAA hurricane hunter aircraft N43RF on Thursday afternoon, October 22, 2015. At the time, Patricia was a Category 4 storm with 130 mph winds. Image credit: NOAA Hurricane Hunters Facebook Page.


Unfortunately, Patricia is destined to fall in an even smaller group of Category 5s that take aim at Mexico’s Pacific coastline. Most of the intense hurricanes in the Northeast Pacific move along west-northwest tracks that keep them well offshore of Mexico. Apart from the 1959 storm, only two Cat 5s in the Northeast Pacific database have arced northeastward into Mexico: 2009’s Hurricane Rick, which weakened to a tropical storm well before making landfall, and 2002’s Hurricane Kenna, the closest analogue by far to Patricia. Kenna strengthened as it recurved, then weakened only slightly before it plowed into the coast near San Blas as a Category 4 storm. Causing at least four deaths and inflicting around $100 million US in damage, Kenna struck with winds of 140 mph, which made it the second-strongest Pacific storm to strike Mexico in modern records.

The forecast for Patricia
Hurricanes rarely maintain Category 5 status for more than 24 hours, but Patricia has a very good shot at remaining a formidable storm right up to landfall. Along the expected path, sea-surface temperatures are at near-record warm levels (about 30.5°C, or 87°F), and there is enough deep oceanic heat so that even violent Category 5 winds are unlikely to stir up enough cooler water to disrupt the storm (see Figure 5 below). Vertical wind shear has increased to moderate levels (10 - 20 knots), and the shear is predicted to continue increasing on Friday, as Patricia moves into a zone of stronger upper-level southwesterlies that will curve the storm to the right. These winds may also push drier air into the hurricane’s core, which could cause some disruption. Intense hurricanes also tend to go through eyewall replacement cycles after a day or two at peak strength, so it’s quite possible that such a cycle will occur before landfall, which could cut down Patricia’s strength slightly. Even with all these factors taken into account, it seems very probable that Patricia will reach land as at least a Category 4; the NHC’s official forecast updated at 12:30 am EDT Friday brings Patricia onshore as a Category 5.


Figure 5. Oceanic heat content along the general expected path of Hurricane Patricia. Values above 50 kilojoules per square centimeter (yellow) indicate deep warm water, reducing the odds that the strong winds of an intense hurricane will churn up cooler water that might disrupt it. Image credit: RAMMB/CIRA/Colorado State University.


Forecast models did an excellent job of predicting Patricia’s rapid strengthening, and they are in close agreement on the general track over the next several days: a smooth, sharp turn toward the northeast on Friday, followed by rapid motion into the Mexican coast late Friday or early Saturday. This turn has already begun, as Patricia is now moving toward the north-northwest. The exact timing and sharpness of the turn will determine where Patricia makes landfall; by Friday, we should have a more precise sense of the landfall location, which will most likely be somewhere between Puerto Vallarta and Manzanillo. For now, everyone in the hurricane watch area--and especially the warning area--should be extremely prudent and take this storm very seriously. A direct hit on Puerto Vallarta is a possibility, though that outcome is toward the left edge of the various model solutions. Although no hurricanes of this intensity have struck near Puerto Vallarta in modern times, Kenna (which made landfall about 60 miles to the north) wreaked considerable damage on the Puerto Vallarta area, largely from storm surge. If Patricia strikes between Puerto Vallarta and Manzanillo, it would put the city of Manzanillo and the surrounding bay at considerable risk of storm surge.

Along with the immediate coastal threats of storm surge and extreme wind, Patricia will likely produce torrential rain with the risk of life-threatening floods in the mountains and hills to the north and northeast of its path, including parts of Mexican states of Jalisco, Colima, Michoacan and Guerrero. By late in the weekend, Patricia will be racing across southern Texas, exacerbating what may be a very serious flood threat across parts of the state. See our roundup from this afternoon for more on this multi-pronged heavy rain episode over Texas.

Jeff Masters will be filing our next update on Patricia on Friday morning.

Bob Henson

Hurricane

Major Threat to Mexico from Category 4 Patricia

By: Bob Henson , 8:07 PM GMT on October 22, 2015

Turbo-charged Hurricane Patricia is on track to deliver a devastating one-two punch: landfall as a major hurricane on Mexico's Pacific coast, followed by the storm feeding an extreme rainfall event in parts of Texas. Drawing on near record-warm sea-surface temperatures of 30.5°C or 87°F (1-2°C above average), Patricia is also taking advantage of very light wind shear (5 - 10 knots) and rich atmospheric moisture (greater than 70% relative humidity). Within a span of just 27 hours, from 15Z Thursday to 18Z Friday, Patricia metamorphosed from a minimal tropical storm (top sustained winds of 40 mph) to a Category 4 hurricane (130 mph). This puts Patricia among the top rapid intensifiers in the modern record of hurricane monitoring. Stepped Frequency Microwave Radiometer (SFMR) data collected from aboard a NOAA Hurricane Hunter reconnaissance flight confirmed a peak wind of 114 knots (131 mph) on Thursday afternoon near 1:30 pm EDT.


Figure 1. latest visible satellite image for Hurricane Patricia.


Figure 2. Infrared satellite image of Hurricane Patricia taken at 1:45 pm EDT Thursday, October 22, 2015. Image credit: NOAA/NESDIS.

There is no sign of any letup in Patricia’s intensification. A pinhole eye was becoming evident in visible and infrared satellite imagery at midday Thursday (see Figures 1 and 2). Ominously, the rapid intensification index from the SHIPS model on Thursday morning showed a 95 percent chance of Patricia strengthening by another 45 mph over the 24 hours (Patricia’s intensity at that point was estimated at 100 mph). At 2 pm EDT Thursday, the National Hurricane Center projected that Patricia would peak at 150 mph winds by Friday morning--just 10 mph below Category 5 strength--and would strike the Mexican coast as a Category 4 storm. Update: At 8 pm EDT Thursday, Patricia's top sustained winds were already up to 150 mph. Satellite loops suggest that Patricia could be upgraded to Category 5 strength by Friday morning, if not Thursday night.

The track forecast for Patricia
After roughly paralleling the Mexican coast on Thursday, Patricia is expected to make a rapid turn toward the north, bringing it onshore between Puerto Vallarta and Manzanillo on Friday night. Models have edged westward slightly, which reduces the threat of a direct strike on Manzanillo but increases the chance that Puerto Vallarta will experience impacts. On its currently forecast track, Patricia would pass east of Puerto Vallarta after several hours over land, but only a slight westward bend could results in a more direct strike on Puerto Vallarta. Hurricane warnings are in effect from Cabo Corrientes to Punta San Telmo, with a hurricane watch extending east to Lazaro Cardenas. A hurricane watch and tropical storm warning extend west from the warning area to San Blas, including Puerto Vallarta.


Figure 3. Major hurricanes (Category 3, 4, and 5) that have passed within 200 miles of Patricia’s location (15.0°N, 104.0°W as of 2 PM EDT Thursday, October 22, 2005).

Few of the Northeast Pacific’s major hurricanes strike the Mexican coast
Although the Northeast Pacific can be a highly active region for hurricanes, relatively few of these make landfall on the Mexican coast, thanks largely to the coastline’s northwest-to-southeast orientation. Most hurricanes that develop off Mexico’s Pacific coast track west or west-northwest, eventually decaying well out to sea (see Figure 3). However, the exceptions can be devastating. Landfalling hurricanes in this area are most common toward the end of the season, as upper-level westerlies begin to penetrate far enough south to force low-latitude storms to recurve. The last major hurricane to make landfall in the Mexican states under threat from Patricia--Nayarit, Jalisco, and Colima--was Category 4 Hurricane Kenna in late October 2002. Causing at least four deaths and inflicting around $100 million US in damage, Kenna struck with winds of 140 mph, which made it the second-strongest Pacific storm to strike Mexico in modern records. The strongest was an unnamed 1959 hurricane that struck near Manzanillo, also in late October. This catastrophic storm is the only Category 5 hurricane to strike Mexico’s Pacific coast, with estimated peak winds of near 160 mph (but the storm will likely be downgraded to Category 4 status based on a reanalysis now under review.) Damage was $280 million US, which would equate to more than $2 billion in current dollars. Some 1800 deaths were attributed to the storm, making it the deadliest Northeast Pacific hurricane on record.


Figure 4. Predicted rainfall for Hurricane Patricia from the 2 am EDT (06 UTC) Thursday, October 22, 2015 run of the HWRF model. Patricia is predicted to dump widespread rains of 8 - 16" along the coast, and bring a swath of 2 - 4" of rain all the way to South Texas. Image credit: NOAA.

Torrential rains aiming for Texas
Patricia will compound an ongoing heavy rain episode in Texas being driven by the approach of a strong upper-level low. Rich Gulf moisture is pooling along a surface front associated with the upper low. A cluster of heavy storms covered most of western Oklahoma at midday, extending into the west half of North Texas. This slow-moving area is expected to stall tonight and Friday over northern Texas, producing a stripe of rainfall that could total 6” - 8”. The Dallas-Fort Worth area could end up within this belt of heaviest rain. Round Two arrives with the injection of moisture ahead of Hurricane Patricia, whose remnants will be sweeping across Mexico toward Texas this weekend.


Figure 5. 3-day precipitation forecast for the period 0Z Friday, October 23 (7:00 pm EDT Thursday) through 0Z Monday. Image credit: NOAA/NWS Weather Prediction Center.


Figure 6. Latest drought status across Texas as of Tuesday, October 20, as released in the U.S. Drought Monitor on October 22. We can expect much of this red to disappear by next week! Image credit: U.S. Drought Monitor.


Conditions are aligning for a predecessor rain event (PRE) across the heart of Texas as Patricia approaches this weekend. In such events, tropical moisture well out ahead of a landfalling tropical cyclone interacts with a surface front and upper-level trough to produce heavy rainfall, often with significant inland flooding. By Saturday and Sunday, Patricia’s remnants will be moving across southern Texas, exacerbating rainfall there. Multi-day totals for the whole event will depend on where each of the various elements ends up being focused, but central Texas from Dallas to Austin appears to be most at risk for totals that could locally exceed a foot. It’s been a year of rainfall extremity for Texas: May was by far the wettest month in state history, quenching severe drought conditions, while dryness in late summer and early fall put much of the state back into drought (see Figure 6).

Tropical cyclones from the Northeast Pacific are notorious autumn rainmakers in Texas and Oklahoma. In late October 1983, Hurricane Tico caused hundreds of millions in US damage and led to rainfall totals exceeding a foot across parts of northern Texas and southern Oklahoma.


Figure 7. Latest satellite image of Hurricane Olaf.

Two other major hurricanes in the Pacific: Olaf and Champi
Though it’s weakened notably in the last 24 hours, Hurricane Olaf remained a Category 3 storm as of the 11 am EDT Thursday advisory from NHC. Olaf’s recurving path toward the north-northwest will be taking it into increasing shear and over gradually cooler waters over the next several days, leading to a gradual decline. However, Olaf is still projected to be a tropical cyclone on Tuesday morning, October 27, and its remnants will be sweeping toward the U.S. West Coast by midweek. Computer models still differ on Olaf’s evolution at that point, but at minimum, we can expect some of its moisture and energy to be folded into a Pacific Northwest storm, and some associated rainfall as far south as California can’t be ruled out yet.


Figure 8. Latest satellite image of Typhoon Champi.

In the Northwest Pacific, Typhoon Champi continues to rage, with top sustained winds of 115 mph as of the most recent advisory. Champi has become an annular typhoon, with a gigantic eye estimated at 70 miles in diameter (see this Capital Weather Gang feature). Champi will accelerate to the northeast over the next several days, likely maintaining tropical storm intensity through at least Sunday before it gets swept into a powerful, non-tropical storm system in the North Pacific.

Wunderblogger Steve Gregory has an update in his Thursday afternoon post, Heavy Rain in Texas as Progressive Pattern Leads to Increased Forecast Uncertainty.

Bob Henson


Hurricane

September 2015: Earth's Warmest Month in Recorded History, Says NOAA

By: Jeff Masters , 3:40 PM GMT on October 21, 2015

September 2015 had the largest departure of temperature from average of any month among all 1629 months in the record that began in January 1880, said NOAA's National Centers for Environmental Information (NCEI) on Wednesday. (Note that since July and August are typically the warmest months globally in absolute terms, September was not Earth's warmest month in that regard.) NASA rated September 2015 slightly cooler, as the 2nd warmest September on record, falling below September 2014's mark. September 2015's warmth makes the year-to-date period (January - September) the warmest such period on record, according to both NOAA and NASA. September 2015 was the fifth consecutive month a monthly high temperature record has been set in NOAA's database, and the seventh month of the nine months so far in 2015. A potent El Niño event in the Eastern Pacific that crossed the threshold into the "strong" category in early July continues to intensify, and strong El Niño events release a large amount of heat to the atmosphere, typically boosting global temperatures by at least 0.1°C. This extra bump in temperature, when combined with the long-term warming of the planet due to human-caused emissions of heat-trapping gases like carbon dioxide, makes it virtually assured that 2015 will be Earth's second consecutive warmest year on record--with 2016 a good bet to exceed even 2015's warmth.

NOAA's top ten warmest global monthly departures from average
1) 0.90°C, Sep 2015
2) 0.89°C, Aug 2015
2) 0.89°C, Mar 2015
2) 0.89°C, Feb 2015
2) 0.89°C, Jan 2007
6) 0.87°C, Jun 2015
7) 0.86°C, Feb 1998
8) 0.85°C, May 2015
8) 0.85°C, Mar 2010
10) 0.84°C, Dec 2014


Figure 1. Departure of temperature from average for September 2015, the warmest September for the globe since record keeping began in 1880. Record warmth was observed across northeastern Africa stretching into the Middle East, part of southeastern Asia, most of the northern half of South America, and parts of central and eastern North America. Record warmth was also over much of the world's oceans, including the Eastern Mediterranean Sea, most of the Arabian Sea, and the waters surrounding Hawaii, where the warm waters are expected to cause a significant coral bleaching episode resulting in a large-scale die-off of coral. Record warm waters were also observed between the Bahama Islands and Bermuda, which helped fuel Hurricane Joaquin's rapid intensification into a Category 4 storm in mid-September. A loss of 10 - 20% of all coral worldwide over the next few months is expected due to the record warm ocean temperatures causing a global bleaching event. Image credit: National Centers for Environmental Information (NCEI) .

Global satellite-measured temperatures in September 2015 for the lowest 8 km of the atmosphere were tied for 3rd warmest in the 37-year record, according to the University of Alabama Huntsville (UAH), and were the 5th warmest on record, according to RSS. The lowest 8 km of the atmosphere heats up dramatically in response to moderate to strong El Niño events, with a time lag of several months. The two warmest Septembers occurred during the El Niño events of 1998 and 2010.



Three billion-dollar weather disasters in September 2015
Three billion-dollar weather-related disasters hit the Earth last month, according to the September 2015 Catastrophe Report from insurance broker Aon Benfield: wildfires in Indonesia ($4 billion in losses, though more recent estimates put the damage at $14 billion); wildfires in California that cost at least $2 billion; and drought in Western Canada that has cost at least $1 billion through the end of September. With eighteen billion-dollar weather disasters through September 2015, and two more already during the first half of October--flooding in South Carolina of at least $2 billion, and at least $4.2 billion in damage from China's Typhoon Mujigae--Earth is on pace for an average number of such disasters, compared to statistics from the past ten years.


Disaster 1. Multiple wildfires raged across California during much of September, with the Valley Fire, northwest of San Francisco, and the Butte Fire, southeast of Sacramento, the most destructive of the fires. The Valley Fire--the third most damaging in state history, at $1.5 billion--left four people dead and destroyed 1,958 homes and other structures. The Butte Fire left two people dead and destroyed 475 homes, and was the seventh-most damaging wildfire in state history, at $450 million. This year is now the costliest and damaging year for wildfires in the United States since 2007. In this image, we see burned out cars from the Valley Fire's rampage through Lake County, California; the fire started on September 12, 2015. Image credit: wunderphotographer noneinc.


Disaster 2. As discussed in detail in the Jeff Masters October 13 post, "Costliest (and Deadliest?) Disaster of 2015: Indonesia's $14 Billion Fires", the El Niño event of 2015 has brought devastating drought and fires to Indonesia and neighboring countries. This year's fires in Indonesia are on track be their most expensive disaster in history, beating the $9.3 billion price tag of the 1997 - 1998 fires. In this photo, we see buildings blanketed with thick smog in Singapore on September 24, 2015. Singapore's air quality reached 'very unhealthy' levels on September 24, forcing schools to close, as thick smog from agricultural fires in Indonesia's neighboring Sumatra Island choked the city-state. Image credit: ROSLAN RAHMAN/AFP/Getty Images.


Disaster 3. Drought conditions continued to intensify across western Canada during September as a lack of rainfall wreaked havoc on agricultural interests. The province of Alberta was particularly affected, where a disaster was declared after more than 80 percent of farmers reported sustaining crop loss during the year. Damage estimates were $1 billion and growing. In this image, we see smoke from drought-aided forest fires over British Columbia settling into valleys on July 8, 2015. Image credit: NASA.

Arctic sea ice falls to 4th lowest September extent on record
Arctic sea ice extent during September 2015 was the 4th lowest in the 36-year satellite record, according to the National Snow and Ice Data Center (NSIDC). Sea ice extent reached its annual minimum extent on September 11, bottoming out at the 4th lowest extent on record. Unfavorable winds resulted in large losses of thick, multi-year ice in 2015; there was a 31% depletion of the multi-year ice cover this summer for the Arctic as a whole, compared to only 12% in 2013 and 38% during the record sea ice loss year of 2012.

Notable global heat and cold marks set for September 2015
Hottest temperature in the Northern Hemisphere: 47.8°C (118.0°F) at Mitribah, Kuwait, September 15
Coldest temperature in the Northern Hemisphere: -42.8°C (-45.0°F) at Geo Summit, Greenland, September 30
Hottest temperature in the Southern Hemisphere: 43.0°C (109.4°F) at Villamontes, Bolivia, September 15
Coldest temperature in the Southern Hemisphere: -82.9°C (-117.2°F) at Dome Fuji, Antarctica, September 13

Major stations that set (not tied) new all-time heat or cold records in September 2015
Krosno (Poland) max. 34.5°C, September 1
Anguilla Airport (Anguilla, United Kingdom) max. 33.7°C, September 9. New Territorial record high for Anguilla. Improved to 33.8°C on September 12.
Charlotte Amalie (U.S. Virgin Islands,USA) max. 35.6°C, September 11. New Territorial record high for the U.S. Virgin Islands.
Havana (Cuba) max. 38.2°C, September 12
Ibague (Colombia) max. 36.8°C, September 16
Lerida (Colombia) max. 39.4°C, September 22
Goias (Brazil) max. 41.9°C, September 24
Peixe (Brazil) max. 40.7°C, September 26
Posse (Brazil) max. 38.4°C, September 26
Jerusalen (Colombia) max. 41.8°C, September 26
Jabalcon (Colombia) max. 42.4°C, September 27



New all-time national and territorial heat records set or tied in 2015
As of October 15, 2015, fourteen nations or territories tied or set all-time records for their hottest temperature in recorded history in 2015, and two (Israel and Cyprus) set all-time cold temperature records. For comparison, only two nations or territories set all-time heat records in 2014, and nine did in 2013. The most all-time national heat records held by any year is nineteen in 2010. Most nations do not maintain official databases of extreme temperature records, so the national temperature records reported here are in many cases not official. I use as my source for international weather records researcher Maximiliano Herrera, one of the world's top climatologists, who maintains a comprehensive list of extreme temperature records for every nation in the world on his website. If you reproduce this list of extremes, please cite Maximiliano Herrera as the primary source of the weather records. Wunderground's weather historian Christopher C. Burt maintains a database of these national heat and cold records for 235 nations and territories on wunderground.com's extremes page.

Kudos also to Mr. Herrera for supplying the data for the "Notable global heat and cold marks set for September 2015" and "Major stations that set (not tied) new all-time heat or cold records in September 2015" sections.

Jeff Masters

Climate Summaries

Patricia Threatens Mexico; Big Surf in Hawaii From Olaf; Koppu Finally Dies

By: Jeff Masters , 2:02 PM GMT on October 21, 2015

Tropical Storm Patricia formed on Tuesday evening in Mexico's Pacific waters about about 400 miles east-southeast of Acapulco, Mexico, becoming the 16th named storm of this unusually active Eastern Pacific hurricane season. Satellite loops on Wednesday morning showed that Patricia was a poorly organized minimal tropical storm with 40 mph winds, with no well-formed low-level spiral bands and a modest area of heavy thunderstorms. Radar images from the Acapulco radar showed that Patricia's main heavy thunderstorm activity was offshore, though a few bands of heavy rain were affecting the coast. Patricia is under light wind shear, has very warm waters of 30°C (86°F) to work with, and an atmosphere rich in moisture (>80% relative humidity) at mid-levels. These conditions should promote rapid intensification once Patricia gets well-organized and develops an inner core. Patricia will move to the west, roughly parallel to the coast, today through Thursday, then turn abruptly to the north on Friday as it gets pulled northwards by a trough of low pressure. The computer models all agree that this will result in Patricia making landfall in Southwest Mexico on Friday, possibly as a hurricane. If Patricia does make landfall as a hurricane, it would become the fifth latest Pacific hurricane to strike Mexico since records began in 1949, according to a database of Eastern Pacific hurricanes maintained by NOAA's Coastal Services Center. The only Pacific hurricanes to strike Mexico later than October 23 were Category 4 Hurricane Kenna of 2002 (which struck on October 25) and Category 3 Hurricane Olivia of 1975 (also an October 25 landfall), Category 1 Hurricane Rick (November 10, 1997) and Category 1 Hurricane Tara (November 11, 1961.)


Figure 1. Latest satellite image of Patricia.

Central Pacific's Hurricane Olaf maintains Category 4 strength
Hurricane Olaf intensified into a major Category 4 hurricane on Monday at 5 pm EDT in the waters about 1200 miles east-southeast of Hawaii, and maintained Category 4 strength through Wednesday morning at 5 am EDT. Wednesday morning satellite loops showed Olaf was a bit weaker than its 150 mph peak strength on Tuesday, and the storm is likely to continue to weaken as it turns north late this week, passing about 600 miles east of Hawaii on Saturday morning. While the storm will not bring strong winds or heavy rain to the islands, Olaf is generating high surf, and a High Surf Advisory is posted for Hawaii's Big Island for waves of 6 - 10 feet. Latest long-range forecasts from the GFS and European models keep Olaf moving to the northeast next week, away from Hawaii. Some of the long-range outlooks from the GFS model have shown Olaf (or its extratropical remnant) getting unusually close to Northern California 7 - 9 days from now, but these forecasts have not been consistent.


Figure 2. MODIS image of Hurricane Olaf in the waters east-southeast of Hawaii as seen from NASA's Aqua satellite on Tuesday, October 20, 2015. At the time, Olaf was at peak strength--a Category 4 storm with 150 mph winds. Image credit: NASA.

Typhoon Koppu finally dies
High wind shear and interaction with land have finally done in Typhoon Koppu (known as Lando in the Philippines), whose remnants are still bringing some heavy rain to northern Luzon Island in the Philippines. According to BBC News, Koppu killed at least 39 people and left behind $141 million in agricultural damage. Weather.com has a detailed summary of Koppu's impacts on the Philippines.


Figure 3. Thousands of homes were damaged in Casiguaran, Philippines during Typhoon Koppu. (@jeffcanoy/instagram) 

I'll have a new post by 1 pm EDT today, after NOAA releases its global September weather summary.

Hurricane

Koppu Pulling Away from Philippines; TD 20-E May Threaten Mexico

By: Bob Henson and Jeff Masters , 6:03 PM GMT on October 20, 2015

Tropical Storm Koppu (known as Lando in the Philippines) is now arcing slowly around the northern tip of Luzon island after dumping prodigious amounts of rain over the last three days. At 15Z Tuesday (11:00 pm local time), Koppu was located at 19.2°N, 121.0°E, about 40 miles north of the north-central coast of Luzon. Koppu’s top sustained winds were down to 50 mph, but the storm should be able to maintain that strength for the next day as it crawls to the east. This will keep the island in moist westerly flow, so some additional rain is possible over already-soggy areas.


Figure 1. Residents remove mud near their house after heavy rains brought about by Typhoon Koppu inundated homes in Cabanatuan City, Nueva Ecija province, north of Manila on October 20, 2015, days after the typhoon hit Aurora province. Image credit: Ted Aljibe/AFP/Getty Images.


Figure 2. A man paddles a makeshift raft made from banana trunks over a flooded rice field at Barangay Camanutan, Isabela province, north of Manila on October 19, 2015, a day after Typhoon Koppu hit Aurora province. Residents of flooded farming villages in the Philippines were trapped on their rooftops October 19 and animals floated down fast-rising rivers. Image credit: STR/AFP/Getty Images.


Damage over the last three days from Koppu’s landfall and subsequent flooding is still being assessed, but weather.com reports that at least 28 people have died. Nearly all buildings and infrastructure sustained damage in the city of Casiguran, close to where Koppu came ashore. It appears that much of Koppu’s heavy rain stayed just offshore, but the upslope flow against the west side of Luzon’s mountains has been enough to generate immense local amounts, triggering mudslides and floods affecting the mountains as well as adjacent lowlands. The city of Baguio racked up 40.37” of rain through Tuesday afternoon, according to weather.com. A few miles south of Baguio, the massive San Roque Dam (the largest dam in the Philippines, and the world’s twentieth largest) had plenty of water to deal with. Weather records researcher Maximiliano Herrera, who maintains a comprehensive set of extreme temperature records on his website, pulled the following preliminary amounts for San Roque Dam from real-time data collected over a 24-hour period at the height of Koppu.

30 minutes: 66 mm (2.60”)
1 hour: 122 mm (4.80”)
6 hours: 483 mm (19.02”)
12 hours: 717 mm (28.23”)
18 hours: 1093 mm (43.03”)
24 hours: 1317 mm (51.85”)

If confirmed, these would set new 12- and 24-hour rainfall records for the Philippines, beating the records set during a July 1911 typhoon that dumped more than 2200 mm (87”) on Baguio in less than four days. Few other places on Earth have reported heavier amounts for half- and full-day periods. The world records of 1144 mm (45.04”) for 12 hours and 1825 mm (71.85”) for 24 hours were both set at the remote site of Foc-Foc on La Réunion island in the South Indian Ocean on January 7-8, 1966.


Figure 3. Latest satellite image of TD 20-E.

Tropical Depression 20-E forms; expected to hit Mexico as a hurricane
Tropical Depression 20-E formed at 11 am EDT Tuesday in Mexico's Pacific waters about about 445 east-southeast of Acapulco, Mexico, and appears poised to intensify into Hurricane Patricia later this week. TD 20-E is under light wind shear, has very warm waters of 30°C (86°F) to work with, and an atmosphere rich in moisture at mid-levels. These conditions should promote rapid intensification once TD 20-E gets well-organized and develops an inner core. Satellite loops on Tuesday morning showed that TD 20-E was poorly organized, with only a modest area of heavy thunderstorms and just the beginning of low-level spiral bands beginning to form. TD 20-E will move west-northwest, parallel to the coast today through Thursday, then turn abruptly inland to the north on Friday as it gets pulled northwards by a trough of low pressure.


Figure 4. MODIS image of Hurricane Olaf in the waters 1300 east-southeast of Hawaii as seen from NASA's Terra satellite on Monday, October 19, 2015 at 19:35 UTC. At the time, Olaf was a Category 4 storm with 135 mph winds. Image credit: NASA.

Eastern Pacific's Hurricane Olaf hits Category 4
Hurricane Olaf intensified into a major Category 4 hurricane on Monday at 5 pm EDT in the waters about 1200 miles east-southeast of Hawaii, becoming the the Northern Hemisphere's record-setting 21st Category 4 or stronger tropical cyclone of 2015 (previous record: eighteen in 2004, according to wunderblogger Dr. Phil Klotzbach.) Only one of those twenty Category 4 and 5 storms--Hurricane Joaquin--came from the Atlantic. Olaf is also notable for its low latitude. Coincidentally, the two most equatorward Category 4 cyclones on record for the Western Hemisphere share the same name: this year’s Hurricane Olaf (10.0°N) and 2005’s Cyclone Olaf (10.0°S).

By Tuesday morning at 5 am EDT, Olaf’s top sustained winds had increased to 150 mph, where they were holding through 11 am EDT. No other Northeast Pacific storm on record has been this strong any later than September 6, according to Klotzbach and Blake. An additional increase in winds of 10 mph would bring Olaf to Category 5 status, but Tuesday afternoon satellite loops showed a modest warming of the cloud tops, indicating that Olaf had likely peaked in strength. Olaf is likely to turn to the north by this weekend well east of Hawaii. Latest long-range forecasts from the GFS and European models keep Olaf moving to the northeast next week, away from Hawaii.

Accumulated cyclone energy: The Pacific has it
The hyperactive Pacific is reflected in year-to-date statistics on accumulated cyclone energy (ACE) compiled by Phil Klotzbach using data from the National Hurricane Center and Joint Typhoon Warning Center. ACE takes into account the strength as well as the longevity of tropical cyclones, but not their size. Through October 19, the Northeast Pacific ACE (184% of year-to-date average) was on track to end up in second place behind 1992; the Northwest Pacific ACE (189% of year-to-date average) was at record levels for the time of year; and the Central Pacific ACE was at an astounding 606% of its year-to-date average, partly a reflection of the many years that feature little activity in that basin. Within the next day or so, according to Klotzbach, Hurricane Olaf should push the Central Pacific past 1994 to set the basin’s all-time seasonal record. The North Atlantic is at a mere 62% of its year-to-date average, but the prolific Pacific has still pushed the entire Northern Hemisphere to a new year-to-date ACE record as of October 20, says Klotzbach.

Bob Henson and Jeff Masters

Hurricane

Koppu Kills 12, Dumps 30+ Inches of Rain on Philippines; Olaf Hits Category 3

By: Jeff Masters and Bob Henson , 4:43 PM GMT on October 19, 2015

Tropical Storm Koppu has weakened below typhoon strength, but is still bringing dangerous torrential rains to much of the Philippines' Luzon Island as the storm drifts north-northeastwards at 4 mph along the west coast of the island. Koppu, which is known as "Lando" in the Philippines, hit the east-coast province of Aurora around 1:00 am Sunday local time at peak strength, with sustained winds of 150 mph and a central pressure of 920 mb. Fortunately, that part of Luzon is fairly sparsely populated; the death toll from the typhoon stood at a relatively low twelve people on Monday morning. However, damage was reported to nearly 100% of the houses and infrastructure in the city of Casiguran (population 27,000), near where the storm made landfall, and some towns are still cut off from communications. At least 9 million residents of Luzon--close to 10 percent of the population of the Philippines--were without power at the height of the storm on Sunday afternoon local time (midnight Saturday night EDT), according to data from the Philippines National Disaster Risk and Reduction Management Council.


Figure 1. MODIS image of Typhoon Koppu, centered along the west coast of Luzon Island in the Philippines, as seen from NASA's Terra satellite on Monday, October 19, 2015 at 03:05 UTC. At the time, Koppu was a Category 1 storm with 80 mph winds. Image credit: NASA.


Figure 2. A resident carries his rescued piglet near flood-inundated houses at a village in Santa Rosa town, Nueva Ecija province, north of Manila on October 19, 2015, a day after Typhoon Koppu hit Aurora province. Image credit: TED ALJIBE/AFP/Getty Images.

Torrential rains to grip Luzon for several days
Extreme rainfall and flooding remain the main threat from Koppu. Steering currents have collapsed, and the typhoon will move very slowly to the northeast at less than 5 mph over northern Luzon for the next 2 - 4 days. Although Koppu will continue to deteriorate as its center remains over or near land, its broad, strong circulation will keep pulling deep moisture into the island, where upslope flow against higher terrain will squeeze out mammoth amounts of rain. Even a tropical depression can produce enormous rains if it’s moving slowly, especially when positioned near high terrain, and Koppu should maintain at least tropical storm strength the next two days. At a minimum, we can expect widespread storm totals of one to two feet of rain across much of northern Luzon. Multi-day rainfall totals of over two feet will result in widespread flooding and mudslides, and major agricultural damage can be expected as well. It appears the heaviest rains will stay north of the Philippines' most heavily populated region--the capital of Manila--but Koppu could still end up as one of the top-five most costly natural disasters in Philippine history.

Torrential rains in excess of 20" have already hit the city of Baguio, a regional center with about 300,000 residents that’s popular among visitors for its relatively cool climate. Located at an elevation of roughly 5000 feet, but less than 20 miles from Luzon’s west coast, Baguio is highly vulnerable to moist westerly winds being forced upslope. A typhoon in July 1911 dumped more than 2,200 millimeters (87 inches) of rain on the city in less than four days. In September 2015, Typhoon Goni brought more than 700 millimeters (28 inches) of rain to Baguio, even without making a direct hit on the Philippines, as noted by weather.com. Baguio received 6.34" of rain from Koppu in the 24 hours ending at 00 UTC October 19, 2015, then another 15.94" in the twelve hours ending at 12 UTC (8 am EDT) Monday. Another 11.14" fell in the six hours ending at 18 UTC, for a 42-hour rainfall total of 33.42" (849 mm.) Monday morning rainfall forecasts from the HWRF model were projecting another 1 - 2 feet of rain over western Luzon Island from Koppu.

For reference, below are the global and hemisphere records for heaviest rainfall observed in various time periods, as certified by the World Meteorological Organization and archived by Arizona State University.

24 hours: 1.825m (71.8"), January 7-8, 1966, Foc-Foc, La Réunion
48 hours: 2.493m (98.15"), June 15-16, 1995, Cherrapunji, India
72 hours: 3.930m (154.72"), February 24-26, 2007, Cratère Commerson, La Réunion
96 hours: 4.936m (194.33"), February 24-27, 2007, Cratère Commerson, La Réunion


Figure 3. MODIS image of Typhoon Champi as seen from NASA's Terra satellite on Monday, October 19, 2015 at 01:25 UTC. At the time, Champi was a Category 4 storm with 135 mph winds. Image credit: NASA.

Typhoon Champi headed towards Iwo Jima
The Pacific’s relentless tropical season of 2015 continues to amaze. On Sunday, Super Typhoon Champi became the Northern Hemisphere's record-setting twentieth Category 4 or stronger tropical cyclone of 2015 (previous record: eighteen in 2004, according to wunderblogger Dr. Phil Klotzbach.) Only one of those twenty Category 4 and 5 storms--Hurricane Joaquin--came from the Atlantic. Champi is the season’s eighth super typhoon, with winds of at least 150 mph--impressive, but still short of the Northwest Pacific record of eleven super typhoons set in 1965 and matched in 1997.

The only land areas likely to be affected by Champi are Japan’s sparsely populated Volcano Islands, including Iwo Jima (Iwo To). Champi has weakened to a Categery 3 storm, and is forecast by the Joint Typhoon Warning Center (JTWC) to continue to steadily weaken this week, passing very near Iwo Jima as a Category 2 storm near 00 UTC Thursday.


Figure 4. Latest satellite image of Hurricane Olaf.

Eastern Pacific's Hurricane Olaf sets a new record
Hurricane Olaf intensified into a major Category 3 hurricane on Monday at 11 am EDT in the waters about 1350 miles east-southeast of Hawaii, becoming the tenth hurricane and eighth major hurricane of this very busy Eastern Pacific hurricane season. Olaf became a major hurricane unusually far to the south--at 9.9°N latitude, making it the most southerly major hurricane ever observed in the Eastern Pacific since reliable records began in 1971. This year now ties with 2014 and 1992 for the most number of major Eastern Pacific major hurricanes (east of 140°W) in a season--eight. An average Eastern Pacific hurricane season sees 15 named storms, 8 hurricanes, and 3 intense hurricanes, and we have already had 15 named storms, 10 hurricanes, and 8 intense hurricanes so far in 2015. This is the second consecutive year with unusually heavy activity in the Eastern Pacific--in 2014, the basin had 20 named storms, 13 hurricanes, and 8 intense hurricanes, making it the busiest season since 1992, which set records for total number of named storms (24), hurricanes (14), and intense hurricanes (8). It has also been a hyperactive year for hurricanes in the Central Pacific, between 140°W and 180°W. So far in 2015, eight named storms have formed in the Central Pacific, setting a new record for tropical cyclone activity in that basin. According to wunderblogger Dr. Phil Klotzbach, prior to 2015, the previous record for named storms in the North Central Pacific for an entire season was four, set in 1982. This year's record activity in both the Eastern Pacific and Central Pacific has been due to unusually low wind shear and record-warm ocean temperatures caused by the strong El Niño event underway.

Olaf is likely to turn to the north by this weekend well east of Hawaii, but the long-term fate of the storm remains unclear; Hawaii may need to be concerned with Olaf next week.

Invest 97E to bring heavy rains to Mexico's Pacific coast
The Pacific coast of Mexico needs to be concerned with Invest 97E, and area of heavy thunderstorms extending from near the coast of Guatemala westwards along the south coast of Mexico. 97E will track northwestwards to west-northwestwards parallel to Mexico’s Pacific coast for the next several days, far enough offshore to allow for strengthening. In their 8 am EDT Monday Tropical Weather Outlook, the National Hurricane Center gave 97E 2-day and 5-day odds of development of 50% and 80%, respectively.

Low odds of development in the Gulf of Mexico
An area of showers and thunderstorms extending from the northwestern Caribbean Sea through Mexico's Yucatan Peninsula at 8 am EDT Monday was associated with a weak area of low pressure. This low will move slowly west-northwest at about 5 mph, and may emerge over the southern Gulf of Mexico's Bay of Campeche by Wednesday. The disturbance's proximity to land, and presence of 30 knots of wind shear, make development unlikely. In their 8 am EDT Monday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 0% and 10%, respectively. Moisture from the disturbance is likely to spread northwards Wednesday through Friday across the Southern Plains and interact with an upper level low pressure system, bringing heavy rains. Eastern New Mexico, the Texas Panhandle, and the Oklahoma Panhandle could see widespread flooding Wednesday and Thursday, and the flood threat increases late Friday through Sunday for eastern Texas.

Wunderblogger Steve Gregory has an update on El Niño in his Monday afternoon post, Strong Warm-Up on the Way as El Niño Flow Pattern Becomes Firmly Entrenched.

Jeff Masters and Bob Henson


Video 1. Video compilation from James Reynolds of wind damage and flooding associated with Typhoon Koppu, posted on Sunday, October 18, 2015. Image credit: Earth Uncut TV.

Hurricane

Worst Flooding Still to Come in Philippines from Koppu; Champi Now a Super Typhoon

By: Bob Henson , 7:07 PM GMT on October 18, 2015

Although it has weakened to Category 1 strength since making landfall, Typhoon Koppu continues to hold high potential for catastrophic multi-day rainfall in the large Philippines island of Luzon. Koppu edged into the east-coast province of Aurora around 1:00 am Sunday local time as a super typhoon, packing top winds estimated by the Joint Typhoon Warning Center (JTWC) at 150 mph. Fortunately, this part of Luzon is fairly sparsely populated, though two fatalities had been reported by Sunday evening local time. Tree and structural damage and power outages are widespread. At least 9 million residents of Luzon--close to 10 percent of the population of the Philippines--were without power as of Sunday afternoon local time (midnight Saturday night EDT), according to data from the Philippines National Disaster Risk and Reduction Management Council. (Thanks to Nick Wiltgen at the Weather Channel for this statistic.) At 11:00 pm local time Sunday (11:00 am EDT), Koppu was located about 140 miles north-northwest of Manila along the west coast of Luzon. Koppu is known as Lando in the Philippines, which maintains its own naming system for tropical cyclones.

Storm chaser James Reynolds (@EarthUncutTV on Twitter) encountered very high water levels on the Pampanga River north of Cabanatuan, a city of about 270,000 in central Luzon. The embedded YouTube clip at the bottom of this point includes video collected by Reynolds near Cabanatuan and during landfall from the small city of Maddela, just inland from Luzan’s east coast.


Figure 1. MODIS image of Typhoon Koppu over Luzon Island in the Philippines as seen from NASA's Terra satellite on Sunday, October 18, 2015. At the time, Koppu was a Category 2 storm with 105 mph winds. Image credit: NASA.


Figure 2. A man looks at the rising water level of the Magat River caused by continuous rains of Typhoon Koppu at Bayombong, Nueva Viscaya, Philippines, on Sunday, October 18, 2015. Koppu wrecked houses, tore down trees, and unleashed landslides and floods, forcing thousands to flee as it pummeled the northern Philippines on Sunday. Image credit: STR/AFP/Getty Images.


Torrential rains to grip Luzon for several days
The projected track of Koppu is close to a worst-case scenario for catastrophic rainfall across northern Luzon, home to more than 10 million people. Steering currents are collapsing, and the typhoon will be caught in the midst of a broad upper-level ridge, with little to move it out to sea anytime soon. Models agree that the circulation will inch northward over the next 3 to 4 days, either hugging the northwest coast of Luzon or moving along the spine of the island. Although Koppu will continue to deteriorate as its center remains over or near land, its broad, strong circulation will keep pulling deep moisture into the island, where upslope flow against higher terrain will squeeze out mammoth amounts of rain. Even a tropical depression can produce enormous rains if it’s moving slowly, especially when positioned near high terrain, and Koppu should maintain at least tropical storm strength if the center remains just offshore. The 06Z and 12Z Sunday runs of the GFS model keeps the center of Koppu near Luzon until early Friday local time, while the ECMWF pulls Koppu away from the island by Thursday and the UKMET by Wednesday. At a minimum, we can expect widespread storm totals of one to two feet of rain across much of northern Luzon. High-resolution output from the GFS and ECMWF suggest that a few localized multi-day totals in or beyond the 40” - 50” range are conceivable. Widespread flooding and mudslides are virtually certain, and major agricultural damage can be expected as well. It appears the heaviest rains will stay north of Manila, but Koppu could still end up as one of the most costly natural disasters in Philippine history if the predicted rains materialize.


Figure 3. Weak steering flow will be surrounding Typhoon Koppu for several days, exacerbating the risk of heavy rain over the northern Philippines. Shown in this WunderMap image is the flow at 200 mb (about 40,000 feet), labeled in knots, predicted by the 12Z Sunday run of the GFS model for 18Z Tuesday (2 a.m. local time Wednesday).


Figure 4. Five-day precipitation totals (in inches) predicted by the 12Z Sunday run of the GFS model. Localized totals could be much higher than depicted in this coarse-resolution graphic. Image credit: NWS/NCEP.


Some of the heaviest rain may fall in and near the city of Baguio, a regional center with about 300,000 residents that’s popular among visitors for its relatively cool climate. Located at an elevation of roughly 5000 feet, but less than 20 miles from Luzon’s west coast, Baguio is highly vulnerable to moist westerly winds being forced upslope. A typhoon in July 1911 dumped more than 2,200 millimeters (87 inches) of rain on the city in less than four days. In September 2015, Typhoon Goni brought more than 700 millimeters (28 inches) of rain to Baguio, even without making a direct hit on the Philippines, as noted by weather.com.

For reference, below are the global records for heaviest rainfall observed in various time periods, as certified by the World Meteorological Organization and archived by Arizona State University.

24 hours: 1.825m (71.8"), January 7-8, 1966, Foc-Foc, La Réunion
48 hours: 2.493m (98.15"), June 15-16, 1995, Cherrapunji, India
72 hours: 3.930m (154.72"), February 24-26, 2007, Cratère Commerson, La Réunion
96 hours: 4.936m (194.33"), February 24-27, 2007, Cratère Commerson, La Réunion


Figure 5. Infrared satellite image of Super Typhoon Champi, collected at 1630Z (12:30 pm EDT) Sunday, October 18, 2015. Image credit: CIMMS/SSEC/University of Wisconsin.

Another day, another super typhoon: Champi
The Pacific’s relentless tropical season of 2015 continues to amaze. On Saturday, Koppu became the 19th hurricane or typhoon north of the equator to reach Category 4 strength, a new seasonal record for the Northern Hemisphere. On Sunday, Super Typhoon Champi pushed that record to 20, as it bolted from top sustained winds of 115 mph at 0000 GMT Sunday to 150 mph at 1200 GMT Sunday. (Only one of those Category 4 and 5 storms--Hurricane Joaquin--came from the Atlantic.) Champi is the season’s ninth super typhoon--impressive, but still short of the Northwest Pacific record of 11 super typhoons set in 1965 and matched in 1997.

The only land areas likely to be affected by Champi are Japan’s sparsely populated Volcano Islands, including Iwo Jima (Iwo To). Late Sunday night, Champi was moving slowly northward in the open Northwest Pacific, more than 300 miles south-southwest of Iwo Jima. Champi is forecast by the JTWC to reach Category 5 status by Monday; it should recurve near Iwo Jima as a weakening but still powerful typhoon on Wednesday.

92L running aground in Mexico
Invest 92L should be dissipating soon as it moves onto the southern shores of the Bay of Campeche. Moisture flowing the vicinity of 92L will help fuel heavy rains across Texas later this week, and the decaying system may also feed the development of Invest 97E, just south of the Gulf of Tehuantepec. 97E will track northwest parallel to Mexico’s Pacific coast for the next several days, far enough offshore to allow for strengthening. The National Hurricane Center gives 97E a 40 percent chance of development by Tuesday and an 80 percent chance by Friday. Further west, newly designated Hurricane Olaf will churn harmlessly well out to sea, possibly reaching Category 3 strength by Tuesday before it begins to weaken later in the week.

Bob Henson


Video 1. Video compilation from James Reynolds of wind damage and flooding associated with Typhoon Koppu, posted on Sunday, October 18, 2015. Image credit: Earth Uncut TV.



Hurricane

Super Typhoon Koppu Could Hit Philippines as a Cat 5

By: Jeff Masters , 4:13 PM GMT on October 17, 2015

Intensifying Super Typhoon Koppu is pounding the Philippines' eastern Luzon Island with torrential rains as the storm crawls west-northwest at 6 mph. Koppu (called "Lando" locally in the Philippines) could achieve Category 5 status before making landfall between 2 - 6 pm EDT Saturday. At 8 am EDT Saturday, the Joint Typhoon Warning Center estimated Koppu was a Category 4 super typhoon with top winds of 150 mph, and the Japan Meteorological Agency estimated a central pressure of 930 mb. According to wunderblogger Dr. Phil Klotzbach, Koppu is the nineteenth Category 4 or 5 tropical cyclone this year in the Northern Hemisphere, setting a new record for these most powerful of storms. The previous record was eighteen such storms in 2004. Satellite loops on Saturday morning showed that Koppu had an impressive ring of eyewall clouds with very cold cloud tops that extended high into the atmosphere, and a prominent 23-mile diameter eye. The combination of low wind shear, warm ocean waters that extend to great depth and the presence of two impressive upper level outflow channels will support continued intensification right up until landfall. Extreme winds, a large storm surge, and heavy rains are all major threats from Koppu, but it is the storm's rains that will cause most of the storm's destruction. Recent satellite estimates showed Koppu's maximum rainfall rate was likely 20 inches of rain per 24 hours.


Figure 1. Typhoon Koppu as seen by Japan's Himawari satellite on Saturday, October 17, 2015 at 02:19 UTC (10:19 pm EDT Friday.) At the time, Koppu was an intensifying Category 3 storm with 120 mph winds. Image credit: NOAA/RAMMB and Japan Meteorological Agency.


Figure 2. Super Typhoon Koppu as seen by Philippines radar at 11:15 am EDT Saturday, October 17, 2015. Image credit: PAGASA.

Forecast for Koppu: an extreme rainfall nightmare
Unfortunately for the Philippines, Koppu is moving very slowly, which will lead to extremely high rainfall rates. Koppu will slow down further after landfall, and spend at least three days over northern Luzon Island. With water temperatures an unusually warm 30 - 31°C (86 - 88°F) in the waters surrounding Luzon--about 1°C (1.8°F) above average--the typhoon will be able to pull in tremendous amounts of water vapor from the oceans, resulting in widespread rains of over two feet falling on Luzon Island. More than four feet of rain will likely fall in some mountainous areas, and rainfall amounts of this magnitude are likely to cause devastating flooding. The latest 06Z (2 am EDT) Saturday run of the GFS model shows Koppu spending a full five days over Luzon, which would result in even more disastrous rainfall amounts than described here. The capital of Manila (population 12 million) lies right at the edge of where the most extreme rains of at least a foot will fall, so hopefully the monetary damage from the flooding will stay below a billion dollars.


Figure 3. Predicted rainfall (inches) for the 24-hour period 2 am EDT Saturday - 2 am EDT Sunday, October 18, 2015, based on satellite-derived rainfall estimates. An area of more than 20 inches of rain in 24 hours (pink colors) was predicted just offshore of the Philippines' Luzon Island. Image credit: NOAA/NESDIS.


Figure 4. Predicted 5-day rainfall amounts from Typhoon Koppu from the 00Z Saturday (8 pm EDT Friday) October 17, 2015 run of the GFDL model. Widespread rainfall amounts in excess of two feet (orange and red colors) were predicted for the Philippines' Luzon Island, north of the capital of Manila. Image credit: NOAA/GFDL.

Best historical analogue for Koppu's rains: the historic rains of August, 2013
The best historical analogue for the rains expected from Koppu may be an extreme monsoon rainfall event on August 18 - 21, 2013, which was enhanced by moisture from Tropical Storm Trami. Up to 600 millimeters (23.5 inches) of rain fell during one 24-hour stretch, and about 60% of metro Manila was under water at one point. At least 27 people died, and damage was estimated at $2.2 billion, making it the Philippines' second most expensive disaster in their history. Another possible analogue: a 1911 typhoon dumped more than 2,200 millimeters (87 inches) of rain in four days in Baguio, in a mountainous region of Luzon Island, according to TWC's Nick Wiltgen.

The top five most expensive disasters in Philippines history, according to EM-DAT (dollar values unadjusted for inflation):

1) Super Typhoon Haiyan, 11/8/2013, $10 billion
2) Monsoon rains increased by Tropical Storm Trami, 8/20/2013, $2.19 billion
3) Super Typhoon Bopha, 12/4/2012, $898 million
4) Super Typhoon Rammasun, 7/15/2014, $821 million
5) Tropical Storm Nina, 9/4/1995, $700 million

Storm chaser James Reynolds is on Luzon, and will be posting updates on his experiences via his Twitter feed.

Elsewhere in the Pacific: Typhoon Champi, Tropical Storm Olaf, and Tropical Cyclone Two
Category 2 Typhoon Champi is expected to intensify into a Category 4 storm by Sunday, becoming the Northern Hemisphere's record-setting twentieth Category 4 or stronger tropical cyclone of 2015. Champi is headed northwest, and will turn to the north and northeast on Sunday and Monday. By Tuesday, a weakening Champi may pass close enough to Iwo Jima to bring hurricane-force winds to that island.

In the Eastern Pacific, Tropical Storm Olaf is steadily organizing as it heads west at 12 mph towards Hawaii. Olaf is predicted to reach major hurricane strength by Monday, but will turn to the northwest well before reaching Hawaii, eventually dying in the waters between Hawaii and California more than a week from now. Olaf is not a threat to any land areas.

In the South Pacific, Tropical Cyclone Two, the second tropical cyclone of the 2015 - 2016 season, is expected to dissipate in the waters about 300 miles west of Fiji on Saturday night.


Figure 5. Latest satellite image of 92L.

Development of 92L in Gulf of Mexico possible
An area of showers and thunderstorms (Invest 92L) extending from the northwestern Caribbean Sea through the southern Yucatan Peninsula at 8 am EDT Saturday was associated with an area of low pressure located over central Belize. This low will move slowly west-northwest at about 5 mph, and may emerge over the southern Gulf of Mexico's Bay of Campeche on Sunday or Monday. The disturbance's proximity to land, and competition from a separate tropical disturbance in the Eastern Pacific that NHC is giving 5-day development odds of 80% to, will keep the odds of 92L's development low. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave 92L 2-day and 5-day odds of development of 10% and 20%, respectively. Moisture from 92L is likely to spread northwards across Texas late in the week, bringing heavy rains.

Jeff Masters

Disastrous Rains Possible in Philippines from Typhoon Koppu; Mudslides Wallop SoCal

By: Jeff Masters and Bob Henson , 5:43 PM GMT on October 16, 2015

Heavy rains have begun on the Philippines' main island of Luzon as intensifying Typhoon Koppu heads west-northwest at 11 mph towards the Philippines. At 8 am EDT Friday, Koppu was a Category 2 storm with 105 mph winds, and satellite loops showed that Koppu had an impressive ring of eyewall clouds with very cold cloud tops that extended high into the atmosphere. The combination of low wind shear, warm ocean waters that extend to great depth and the presence of two impressive upper level outflow channels make it likely that Koppu will rapidly intensify to Category 4 status before landfall occurs near 18 UTC (2 pm EDT) Saturday on Luzon. Unfortunately for the Philippines, Koppu will then slow and turn to the north as the storm begins to feel the steering influence of a trough of low pressure passing to its north, and the center of the storm is likely to spend 2 - 2.5 days over Luzon before finally emerging to the north of Luzon on Monday or Tuesday. This will subject the island to an extended period of torrential rains, and some truly prodigious amounts of rainfall are being predicted. The 06Z (2 am EDT) Friday runs of the both the HWRF and GFDL models predicted that Koppu would intensify to Category 4 strength before making landfall, and showed large areas of 24+ inches of rain for Luzon over the next five days. The capital of Manila (population 12 million) was near the southern boundary of the predicted 12-inch rainfall totals. While rainfall forecasts from these two models are often overdone by 50%, it appears likely that a historic rainfall event is likely for the Philippines. Expect widespread damaging flooding capable of causing a top-five most expensive disaster in Philippine history.



Figure 1. Typhoon Koppu (left) and Typhoon Champi (right) as seen by Japan's Himawari satellite on Friday, October 16, 2015. Image credit: Japan Meteorological Agency.


Figure 2. Latest satellite image of Typhoon Koppu.


Figure 3. Predicted 5-day rainfall amounts from Typhoon Koppu from the 06Z (2 am EDT) Friday, October 16, 2015 run of the GFDL model. Widespread rainfall amounts in excess of two feet (orange and red colors) were predicted for the Philippines' Luzon Island, north of the capital of Manila. Image credit: NOAA/GFDL.

Best historical analogue for Koppu's rains: the historic rains of August, 2013?
The best historical analogue for the rains expected from Koppu may be an extreme monsoon rainfall event on August 18 - 21, 2013, which was enhanced by moisture from Tropical Storm Trami. Up to 600 millimeters (23.5 inches) of rain fell during one 24-hour stretch, and about 60% of metro Manila was under water at one point. At least 27 people died, and damage was estimated at $2.2 billion, making it the Philippines' second most expensive disaster in their history.

The top five most expensive disasters in Philippines history, according to EM-DAT (dollar values unadjusted for inflation):

1) Super Typhoon Haiyan, 11/8/2013, $10 billion
2) Monsoon rains increased by Tropical Storm Trami, 8/20/2013, $2.19 billion
3) Super Typhoon Bopha, 12/4/2012, $898 million
4) Super Typhoon Rammasun, 7/15/2014, $821 million
5) Tropical Storm Nina, 9/4/1995, $700 million

Elsewhere in the Pacific: Typhoon Champi, TD 19E, and Tropical Cyclone Two
Category 1 Typhoon Champi passed through the Northern Mariana Islands early Friday, and is expected to intensify into a Category 3 storm and turn to the north by Sunday. By Tuesday, a weakening Champi may pass close enough to Iwo Jima to bring tropical storm-force winds to that island.

In the Eastern Pacific, Tropical Depression 19E is slowly organizing as it heads west at 16 mph towards Hawaii. TD 19E is predicted to reach hurricane strength by Monday, but will turn to the north well before reaching Hawaii, eventually dying in the waters between Hawaii and California late next week. TD 19E is not a threat to any land areas.

In the South Pacific, Tropical Cyclone Two, the second tropical cyclone of the 2015 - 2016 season, has formed in the waters about 300 miles north of Fiji. High wind shear is expected to tear TC Two apart by Sunday.

Tropical development in Gulf, heavy rains on Gulf Coast possible late next week
Our leading models for predicting tropical cyclone genesis are becoming more insistent that a tropical disturbance could develop in the Bay of Campeche toward the latter part of next week, possibly moving into the Gulf of Mexico. The last several sets of GFS ensembles support the idea of tropical or subtropical development in this area, and the 00Z Friday operational runs of the GFS, ECMWF, and UKMET models show potential for least slow, modest development late next week and beyond. The focal point is a sharp cold front that moved across the Gulf of Mexico this week. As the front stalls and slowly returns north as a warm front over the next week, an area of disturbed weather should gradually move from the northwest Caribbean toward the Bay of Campeche, where low pressure of some type may begin to consolidate. In October and November, the most likely areas for Atlantic tropical cyclone formation shift from the open Atlantic to the Caribbean and southern Gulf, so the scenarios painted by the models agree fairly well with climatology. Often these cyclones form along decaying frontal systems pushed into the region by the first large, cool Canadian air masses of the autumn.


Figure 4. A large area of rich moisture and disturbed weather, designated Invest 92L by NHC on Friday afternoon, now covers much of the northwest Caribbean, as shown in this infrared satellite image from 1445Z (10:45 am EDT) Friday, October 16, 2015. Image credit: NOAA/NHC.

Next week’s projected development would be aided to some extent by a strong upper low settling into the southwestern U.S. early next week. This low is predicted to cut off over southern Arizona late in the week before moving northeast into the central U.S. It’s too soon to know whether any development in the Gulf would be tropical or subtropical, but the time of year and projected values of wind shear would tend to favor the latter, especially if strong jet-stream winds associated with the low manage to extend as far east as the western Gulf. Sea-surface temperatures, though cooling with the season, remain warm enough to support tropical or subtropical development over most of the Gulf. Any system that does develop would most likely track toward the north or northeast, steered by the flow between the upper low over Arizona and a strong upper-level ridge over the central Gulf. If model trends are any indication, this could be a very slow-moving feature. Should the area of low pressure stay too close to the western Gulf Coast--a possibility strongly suggested by the models--then interaction with land would hinder tropical development. Another potential complication would be any tropical development in the Pacific just south of the Bay of Campeche, as suggested by the 00Z Friday run of the ECMWF.

Apart from any tropical development, the overall set-up and its slow evolution will support a prolonged period of heavy rain over and near the western Gulf. Rains should begin early next week along the Texas coast, potentially shifting into the central Gulf Coast later in the week. The 7-day precipitation forecast from the NOAA Weather Prediction Center is already calling for 1” – 3” from Houston to Brownsville through Friday, October 23, with most of that projected to fall from Monday onward.



Figure 5. Vehicles are stopped in mud on California's Interstate 5 after flooding Thursday, Oct. 15, 2015. Image credit: Caltrans, via AP.

Southern California walloped by heavy thunderstorms, mudslides
Parts of Interstate 5 were still closed on Friday morning after an intense cluster of thunderstorms dumped torrential rain in the Antelope Valley just north of the Los Angeles metro area on Thursday afternoon. The rains took out several roads and generated mudslides and floods that engulfed nearly 200 vehicles on a state highway east of Tehachapi in mud up to 20 feet deep. Some motorists stayed in their vehicles overnight. No injuries were reported, but the road closures are a major headache for this populous, auto-dependent region. The mudslides and floods (dramatically captured by traffic helicopters) also serve as an unsettling preview of what we might expect from the heavy rains El Niño will likely bring to the region this winter.

Thursday’s intense thunderstorms--large and strong enough to resemble a Midwestern mesoscale convective complex--produced golf-ball-sized hail and thousands of lightning strikes along with torrential rain. The storms were triggered by a tenacious upper-low located just off the Southern California coast. This low carried out a very unusual 12-day loop-de-loop over the last few days, moving in clockwise fashion from Southern California on October 5 to the El Paso area by October 8, Baja California by October 10, well offshore by October 13, and then back around to Southern California. Meanwhile, low-level winds pumped very sultry air into the region over several days; this air mass became highly unstable as it was overtopped by cold upper-level air associated with the upper low. On Wednesday morning, dew point temperatures (which indicate the amount of water vapor in the surface air) hit 69°F in downtown Los Angeles and 72°F in San Diego’s Lindbergh Field—very high values for both locations. Record- or near-record warm sea-surface temperatures from the Southern California coast to Hawaii, partly associated with El Niño, are helping push up moisture values across the region.


Figure 6. Powerful thunderstorms are clustered just north of Los Angeles in this visible satellite image from 2310 GMT (4:10 pm PDT) Thursday, October 15, 2015. Image credit: NEXLAB/College of DuPage.

Two-day precipitation totals ending at 6:00 pm PDT Thursday included 2.37” at Poppy Park and 3.58” at Leona Valley in northern LA County. Rainfall rates near Leona Valley were briefly as high as 4”-6” per hour. While the storms raged, it was fairly tranquil on the other side of the San Gabriel Mountains: no rain was reported in either Los Angeles or San Diego.

Flash flood watches and warnings remained in effect on Friday for large parts of Southern California east and north of the LA Basin. Normally parched Death Valley was under a flash flood warning Friday morning for the second consecutive day. Death Valley’s Furnace Creek observation site received 0.70” of rain this month through Tuesday. Data for Wednesday and Thursday are unavailable, but it is possible Furnace Creek is approaching or has already topped its all-time October rainfall record (1.09”, from 1972). Thanks to weather.com’s Jon Erdman and Nick Wiltgen for details on the Death Valley rains. The embedded Facebook clip below shows flooding on Thursday in the Tehachapi area north of Los Angeles.

Wunderblogger Steve Gregory has more to say on the situation in his Friday afternoon post.

Jeff Masters and Bob Henson

Posted by Jose Antonio Vargas on Thursday, October 15, 2015



Hurricane Flood

NOAA Winter Outlook: El Niño a Dominant Player, but Wild Cards Still Possible

By: Bob Henson , 7:54 PM GMT on October 15, 2015

There’s no missing the influence of El Niño on NOAA’s winter outlook for 2015-16, which was released on Thursday morning. The odds are heavily weighted toward the types of winter weather prevalent during the very strongest El Niño events. The ongoing El Niño is solidly in the top three since 1950, a bit weaker than the record-setting 1997–98 event but stronger than the 1982–83 event.


Figure 1. NOAA’s outlook for winter temperatures (top) and precipitation (bottom) for the three-month period from December 2015 to February 2016. NOAA outlooks are expressed as probabilities for above- or below-average conditions. In the three-class system used by NOAA, an area labeled “equal chances” means that there’s roughly a 33% chance each of below-, near-, or above-average outcomes. If a location is shown with higher odds of above-average conditions, then the probability for below-average outcomes goes down proportionally (e.g., 50% above-average, 33% near-average, and 17% below-average). See NOAA’s online reference guide for more details.

In a nutshell: Wet and cool South, mild and dry North
The enhanced subtropical jet streams common during El Niño tend to boost precipitation across the U.S. Sunbelt and decrease it toward the northern tier of states, as reflected in Figure 1. The same dynamics act to “smoosh out” temperature contrasts across the nation: the cloudy, wet conditions across the South are often accompanied by chilly temperatures, while the drier conditions toward the Northern Rockies are often joined by relatively mild air. NOAA’s Mike Halpert said at a Thursday-morning teleconference that the forecast implies about 2% fewer heating degree days than average. This would also be about 6% fewer days than last winter, he added.

A couple of key caveats:

—NOAA’s probabilities are not meant to imply any judgment on how intense an outcome might be. They’re simply showing where unusually cool, mild, wet, or dry conditions may prevail. Higher odds for those outcomes don’t necessarily mean that the results will be more dramatic than in other areas.

—As the name implies, the seasonal outlooks are meant to convey conditions for the three-month winter period as a whole. They aren't designed to show how much variability there could be across those three months, and of course weather can vary a great deal within a 90-day period.

With that in mind, let’s look at a few potential regional wild cards around the contiguous 48 states. (Warmer- and drier-than-average conditions are good bets for both Hawaii and Alaska.) For more detail on how El Niño affects various parts of the nation, see our roundups published on July 28 and July 30.

California
The strongest El Niño events—like the one now in place--are closely linked to wet winter conditions, especially over Southern California. In both 1982-83 and 1997-98, California arguably got too much of a good thing, with mudslides and floods causing millions in damage. In his October blog post, WU weather historian Chris Burt takes a close look at how those two seasons panned out. One important element will be the temperatures that accompany any big winter storms. If they’re on the warm side—a big problem in recent years—then the snowpack accumulating over the Sierra Nevada could end up disappointingly low. Regardless, aquifers and ecosystems stand to benefit big time if El Niño produces as expected. Overall, this winter offers the best chance in years for California to make up some (though not all) of the hydrologic ground it’s lost during the severe drought in place since 2011. Residents will need to keep calm and carry on for a while longer, though, as the parade of storms common during strong El Niños often doesn’t arrive until December or even January. And crucially, even high odds aren’t the same as a guarantee. While the mega-El Niños of 1982-83 and 1997-98 were both very good to California in terms of precipitation, one of the three next-strongest events (1965-66) fell below average in winter precipitation for all but southern California. You can see how El Niños of various strengths performed at Jan Null’s excellent website on El Niño and California precipitation.

Pacific Northwest
This region is heading into the El Niño of 2015-16 after a dry winter and a very warm, dry summer. Unfortunately, one of the most dependable outcomes of a strong El Niño is winter warmth and dryness from Oregon and Washington into Montana. So the region could go into spring and summer 2016 with even more water worries than last year.

The South
Drab winter weather—chilly and damp—is likely to prevail from Texas to the Southeast coast in 2015-16. The risk of severe weather may be boosted along the immediate Gulf and southeast Atlantic coastal areas. Florida, in particular, needs to watch the skies this winter, as strong El Niño events are associated with a heightened risk of tornado outbreaks, as in the deadly Kissimmee outbreak of February 1998.

The Midwest and Northeast
Tucked inside the somewhat equivocal NOAA outlook for this region is some important nuance. The 1982-83 and 1997-98 El Niños both led to a vast swath of warm winter conditions covering much of Canada and the northern United States, all the way from the Northern Plains to New England. Given the long-term trend toward warmer global temperatures, some truly impressive “warm waves” seem likely to take shape in this area. At the same time, the last few winters have been surprisingly cold and snowy over parts of the Midwest and Northeast. Various experts attribute this to the reverberations of unusually warm water in parts of the tropical Atlantic, the presence in some years of a negative North Atlantic Oscillation (NAO), and/or the loss of Arctic sea ice. We don’t yet know how all of these factors will line up for 2015-16, but I would cast my lot on a mixed-bag winter from the mid-Atlantic to New England, with periods of marked warmth punctuated by occasional sharp but transient cold blasts. Those could end up producing at least one big snowstorm if a negative NAO enters the picture. A good case in point is the winter of 1982-83, when a comparably strong El Niño was in place. Though the winter of 1982-83 averaged quite mild in the Northeast, it also produced the crippling Megapolitan snowstorm of February 10-12, 1983, which dumped 20” – 30” in northwestern suburbs from Washington to Boston. Below is a “blast from the past” YouTube audio clip of a KYW radio newscast from the Philadelphia area during the height of the storm.

Bob Henson


long range winter outlook El Niño Winter Weather

Blob Watch: The Latest on the Northeast Pacific’s Unusual Warmth

By: Bob Henson , 6:17 PM GMT on October 14, 2015

A huge swath of ocean, extending from Hawaii to Baja California and north to the Alaskan coast, has been dominated for much of 2015 by unusually warm sea-surface temperatures (SSTs). In part of the North Pacific, the warm temperatures extend back more than two years. The region that’s come to be known as “The Blob” is more than just a fixed pool of warm water: it’s a dynamic entity that’s been shape-shifting throughout the last couple of years. Persistent as it’s been, The Blob may get a death blow this winter from El Niño.

What exactly is The Blob?
During the winter of 2013-14, researcher Nicholas Bond (University of Washington) noticed a large pool of unusually warm water based in the south central Gulf of Alaska. Within the topmost 300 feet of the ocean, temperatures were as much as 2.5°C (4.0°F) above average in February 2014. By springtime, this warmth had spread east to the coasts of Washington and Oregon. In a report to the Washington state climatologist, Bond dubbed the region of unusually warm water “The Blob.”


Figure 1. Sea-surface temperature anomalies (departures from average) for February 2014 compared to 1981 – 2010. The inner rectangle shows the area analyzed in Nick Bond’s 2015 GRL paper, straddling the region from 135°W to 150°W longitude and 40°N to 50°N longitude. Image credit: American Geophysical Union, used with permission from “Causes and impacts of the 2014 warm anomaly in the NE Pacific,” Geophysical Research Letters, Nicholas Bond et al., doi:10.1002/2015GL063306.


The Blob had its origins in the preceding winter of 2012-13, but Bond found its signature was considerably stronger in 2013-14. By late 2014, two other regions of warmth had developed, one in the Bering Sea and another in the subtropics off Baja California and Mexico. The Blob’s warm anomalies (departures from average) expanded further in 2015, spreading southward toward the equator while growing in east-west breadth. Meanwhile, El Niño began to generate its classic signature of warm water along the equatorial eastern Pacific, just south of The Blob, by the middle of the year. (See this loop of SST anomalies over the past 52 weeks, produced by NOAA’s Earth Systems Research Laboratory.)

The most recent analyses show that the original Blob is now part of a broader east-west zone of warmer-than-normal SSTs that extends west from the Aleutians to the Washington/British Columbia coast. Another zone of even greater warm anomalies runs across the subtropical Pacific from near Hawaii to the California/Mexico coast. Thirdly, along the equator, warmer-than-average SSTs prevail from the International Data Line to the South American coast. El Niño is clearly responsible for the band of equatorial warmth, and at least some of the subtropical warmth, which has fueled record-smashing hurricane activity across the Central Pacific. As for the higher-latitude Blob, that's another matter.


Figure 2. SST anomalies (departures from average) for the period from September 13, 2015 to October 10, 2015. The area analyzed in the inset box of Figure 1 is shown here as a black rectangle south of Alaska. Image credit: NOAA/ESRL/PSD Map Room.


What led to The Blob?
High surface pressure and light winds helped produce the original midlatitude Blob. The persistence of the high pressure at both surface and upper levels was dubbed the Ridiculously Resilient Ridge of 2013 in December of that year by Stanford University doctoral student Daniel Swain at his California Weather Blog. Like the Blob itself, the Ridge persisted as an identifiable feature during 2014 and 2015 as its location evolved. Swain also related the Ridge to the intensification of the ferocious multi-year drought that began in 2011 in California.

The Ridge and the Drought have close family ties. For the study area shown by the rectangle in Figure 1, Nick Bond found that the sea level pressure averaged from October 2013 through January 2014 was higher than for any Oct-Jan period since records began in 1949, and surface wind speeds were the second lowest on record. This relative lack of storminess reduced the amount of mixing between atmosphere and ocean and limited the amount of colder water flowing into the region from the north. In turn, this helped keep surface water over the Blob region from cooling as much as it usually would in autumn and early winter.

During the winter of 2014-15, storms continued to track far to the north across western Canada, again leaving the West Coast largely high and dry and allowing the Blob to gradually expand.

How exactly do the Blob and the Ridge relate to each other?
Experts tend to see the Blob and Ridge as closely connected, but likely triggered by something else. Here’s one leading explanation: back in July, we discussed a recent paper by Dennis Hartmann (University of Washington), who teased out apparent connections during the winter of 2013-14 between warm tropical SSTs west of the Date Line, the Ridiculously Resilient Ridge, and the cold, stormy conditions over parts of the Midwest and Northeast. Hartmann related this chain of events to the North Pacific Mode, a semi-cyclic pattern that helps explain multiyear variations in SSTs over the Pacific. Though many experts believe the tropical Pacific is the ultimate driver of the Ridge and Blob, others have pointed to potential higher-latitude involvement. Research by Jennifer Francis (Rutgers University) has examined the possible influence of Arctic sea ice on the Ridge and other “stuck” midlatitude weather features.

“The Blob and the Ridge most likely had a common etiology,” Swain told me in an email. “It's possible that, once present, the Blob exerted a reinforcing influence on the Ridge, and so there's some possibility that the presence of the Blob enhanced the resilience of the Ridge. But it seems pretty unlikely that the Blob itself was the cause of the Ridge, and so its presence or absence this year probably isn't very relevant for the kind of circulation pattern we are likely to see this winter.”

What happens to the Blob and Ridge this winter?
Strong El Niño events, like the one now in place, tend to generate big winter storms across the Northeast Pacific. Forecast models already show an intensifying parade of storm systems over the Aleutians and Gulf of Alaska for the latter half of October. Over time, the wind and waves from these and subsequent storms should act to erode the original midlatitude Blob. “I feel confident that a strong El Niño event will cool things in a large area around the Date Line and 40°N this winter,” Dennis Hartmann told me in an email. However, SSTs along the immediate coast from California to British Columbia may actually remain well above average this winter. That’s because powerful storms in the Northeast Pacific would tend to foster strong south winds near the coast. Waters near the surface tend to move to the right of the winds above (a process called Ekman transport), so the strong south winds would tend to push warmer water toward the coast and suppress any upwelling of cooler water.

The subtropical warm waters from Hawaii to California could take longer to scour out, as they’re partially a product of the El Niño that will likely remain in place through most or all of the winter. We can expect this southern blob-like feature to help provide warm, moist air for any Northeast Pacific storms that dive toward California. Figure 3 shows how this feature is considerably larger and stronger than it was during the similar El Niño event of late 1997.


Figure 3. Comparison of sea-surface height anomalies (departures from average) measured in late September 1997 (top) and 2015 (bottom), during the onset of comparably strong El Niño events. These images were created from data collected by the TOPEX/Poseidon (1997) and the OSTM/Jason-2 (2015) satellites, using space-based radar altimetry. High sea-surface heights indicate warmer-than-usual water. To create an apples-to-apples comparision, these images were processed by NASA to highlight the year-to-year signal, with seasonal signals and trends removed. Image credit: NASA/JPL.


“It's clear these warm waters have already been influencing weather conditions so far this summer (with an incredible number of Pacific hurricanes, including several that have recurved further northward than we've seen in years),” Swain pointed out. “Persistently warm to hot conditions--along with extremely high dewpoints and even some occasional thunderstorm-related downpours very uncharacteristic of the region--have been occurring across Southern California for months now.”

Swain added: “Ocean surface temperature anomalies of just a few degrees have the potential to add a lot of extra ‘juice’ to incoming Pacific storms this winter. That's yet another reason why it's important not to discount the increased risk of flooding this winter even as California approaches its fifth year since extreme drought began.” Another big question mark is whether any storms that sweep as far north as central California will dump more rain than snow over the Sierra Nevada, where snowpack storage is crucial for the next year’s water supply in California.

Nick Bond is already looking further ahead. “The big question, in my mind, is what happens after the upcoming winter,” Bond said in an email. “Will the weather/wind patterns favor a continuation of the warm ocean conditions, or will there be a switch back to patterns associated with cooler NE Pacific waters?” Recent long-range models suggest that a La Niña could begin emerging in the wake of the current El Niño by mid-2016. If so, that would have a cooling effect on the waters off the U.S. West Coast. Countering this would be any persistence of the Pacific Decadal Oscillation, which entered an apparent warm phase in early 2014. Once it’s in place, a given PDO phase can predominate for more than 20 years, and a warm PDO tends to support warmer-than-usual waters off the U.S. West Coast. Added to all this is the overall long-term warming of both atmosphere and ocean across the planet, which has spiked measurably over the last couple of years (partly due to El Niño).


Figure 4. Ocean sunfish have been observed in both 2014 and 2015 off the southern Alaska coast, hundreds of miles north of their usual habitat. The heaviest bony fish in the world, ocean sunfish prefer waters of 54°F or warmer. Crews from the Alaska Fisheries Science Center caught the large ocean sunfish pictured here. Image credit: AFSC, via NOAA.

The Blob, El Niño, and marine life
Bond noted that any prolonging of the unusual oceanic warmth off the West Coast could have major impacts on native marine ecosystems. Many marine species shift north with El Niño and south with La Niña, but those events typically last just a year or two; the Ridge and Blob have now been in place for more than two years. In breadth and strength, the warming in the North Pacific over the last three years has been the most prolonged since records began in 1900. “Many species can shrug off a bad year or two, but longer runs have greater impacts,” said Bond.

"This El Niño is liable to bring some really strange changes in ocean conditions because the widespread warming of the North Pacific we saw with the blob was so far outside of our experience," said Northwest Fisheries Science Center oceanographer Bill Peterson in a NOAA feature story this month. "When you put an El Niño on top of that it is anyone's guess as to how this will affect marine organisms."

We’ll cover NOAA’s official winter outlook for 2014-15 after its release on Thursday. For a deeper dive into the Blob, check out the excellent article by Eric Simons published last month in Bay Nature. If you prefer your Blobology 101 in cartoon form, below is a fun animation produced by Southern California Public Radio (KPCC); h/t to wunderground member barbamz.

Bob Henson


El Niño Extreme Weather

Costliest (and Deadliest?) Disaster of 2015: Indonesia's $14 Billion Fires

By: Jeff Masters , 4:05 PM GMT on October 13, 2015

Earth's most expensive weather-related disaster of 2015--and the most expensive disaster in Indonesia's history--is underway in that nation, where massive clouds of smoke from agricultural fires have choked the lungs of tens of millions of people for months. Indonesia's Center for International Forestry Research estimated the smoke will cost $14 billion in agriculture production, forest degradation, health, transportation and tourism, according to an October 9 article in The Wall Street Journal. Indonesia's Health Ministry says 20 million people--8% of the country's population--have been impacted by this year's haze; 120,000 of them have sought medical attention for respiratory problems. The disaster may also be the deadliest disaster of 2015, depending upon how one treats the difficult task of determining air pollution deaths. Over 10,000 adults are likely to die from pollution from the fires, judging by the results of a 2013 study in Nature Climate Change by Marlier et al., El Niño and health risks from landscape fire emissions in Southeast Asia. The researchers found that during the strong El Niño year of 1997, the extra smoke in the air in Southeast Asia likely caused an additional 10,800 adult deaths due to cardiovascular disease, and the fires of 2015 are putting a comparable amount of smoke into the air. (Globally, pollution due to fires between 1997 - 2006 was estimated to kill 532,000 people during an average El Niño year--about double the estimated 262,000 deaths that occurred in La Niña years.) Haze from this year's fires is also seriously impacting Malaysia, Singapore, Vietnam and Thailand. The haze in Singapore was so bad that it forced the cancellation of a "zombie apocalypse" competition last month.


Figure 1. Buildings (background) along Shenton way business district are blanketed with thick smog in Singapore on September 24, 2015. Singapore's air quality reached 'very unhealthy' levels on September 24, forcing schools to close, as thick smog from agricultural fires in Indonesia's neighboring Sumatra Island choked the city-state. Image credit: ROSLAN RAHMAN/AFP/Getty Images.


Figure 2. MODIS image of smoke from fires burning in southern Sumatra and Borneo in Indonesia as seen from NASA's Terra satellite at 03:15 UTC September 24, 2015. The red squares are fires detected from the spacecraft. Image credit: NASA.

The culprit: El Niño-driven drought
The warm waters off the Pacific coast of Peru during a strong El Niño episode generate a column of rising air over the tropical Eastern Pacific. Once this rising air reaches the bottom of the stratosphere, which acts as a stable lid preventing further rising motion, the warm air is forced to spread out to the east and west along the Equator. This air eventually sinks over tropical regions well to the east and the west of the Eastern Pacific to complete a huge circulation cell several thousand miles in diameter. Since sinking air warms and dries as it descends, areas of high pressure and drought tend to form in these sinking air regions. To the west of the Eastern Pacific, El Niño events tend to create drought over Indonesia, New Guinea, and Northern Australia; to the east, drought commonly occurs over Northern Brazil. This year's El Niño event is one of the strongest on record, and has led to severe drought in Indonesia. Landowners commonly ignite(mostly illegal) fires to clear land and manage agricultural areas for production of pulp, paper and palm oil in Indonesia. Carbon-rich peatland forests, which are usually too wet to burn, go up in smoke. These peatland fires, which smolder underground, release about three times more smoke than a standard forest fire.


Figure 3. Smoke from huge fires in Indonesia drift westwards all the way to India in this GMS satellite image from NOAA taken at 04:25 UTC October 21, 1997. Image credit: AFP/AFP/Getty Images.

The fires of 2015: comparable to the fires of 1997
Severe drought during the strong 1997 - 1998 El Niño hit Indonesia and neighboring countries, resulting in a series of massive peatland and forest fires that were triggered by slash-and-burn agriculture. The fires produced a noxious yellow haze that covered an area about 2000 by 3000 miles in area for months. Estimates of the economic damage to Indonesia alone were estimated at $9.3 billion by EM-DAT, the international disaster database, making it their most expensive natural disaster in history. The 1997 - 1998 fires were also the most expensive weather-related disaster in the history of Singapore (damages estimated at $9 billion by the Singaporean government, due to increased healthcare costs and disruptions to air travel and business.) According to the 6 November 2002 issue of Nature magazine, the fires in Indonesia released huge amount of carbon dioxide—equivalent to 13 - 40% of the total amount released annually from human burning of fossil fuels. Indonesia's yearly greenhouse gas emissions are somewhat uncertain, due to the large unknowns associated with deforestation and burning of their forests, but the nation may be the world's fifth largest emitter of greenhouse gases. According to an October 9 article at Climate Progress by Samantha Page, land use, including peat and forest fires, accounts for 63 percent of Indonesia’s greenhouse gas emissions. In September 2015, Indonesia promised that it would not increase these emissions over the next 15 years if it receives international support.


Video 1. Greenpeace Indonesia drone video footage showing slash and burn tactics in Indonesia and peat fires in September, 2015. Instead of deep red flames tearing down trees, the smoke is actually emerging from underground from peat that is burning up to 10 metres (33 feet) deep; 40% of this year’s Indonesia fires have been on peatland. Peatland fires were also a major problem in Russia during the record heat wave of 2010.

Wunderblogger Steve Gregory has an update on El Niño and the latest 2-week outlook in his Monday afternoon post.

Jeff Masters

Fire El Niño

A Sizzling October Sunday for Northern Plains

By: Bob Henson and Jeff Masters , 5:22 PM GMT on October 12, 2015

Sweaters and jackets lay dormant, replaced by T-shirts and shorts, for many residents of the United States over the weekend. Temperatures soared into the 80s and 90s across many parts of the country west of the Mississippi River. It wasn’t exactly chilly across the eastern U.S., either, with sunshine and pleasant 60s and 70s the rule over most areas. The most impressive extremes occurred on Sunday over the Northern Plains, where an already-warm airmass from the Rockies warmed even further as west winds pushed it downslope.


Figure 1. High temperatures observed on Sunday, October 11, 2015. Image credit: The Weather Channel.

Even though we’re now into mid-October, when average temperatures are falling fast, several locations managed to break monthly records for heat on Sunday. Many others experienced their warmest (or hottest) day ever recorded so late in the autumn, as catalogued by weather.com. In a number of cases, the readings on Sunday were one to two weeks later than any comparable heat in more than a century of record-keeping.

Locations where Sunday was the warmest day notched so late in the autumn include the following (thanks go to Nick Wiltgen and Linda Lam at weather.com for some of the record-heat data used below):

International Falls, MN: 88°F
Duluth, MN: 84°F
Redwood Falls, MN: 90°F
*Fargo, ND: 97°F
Grand Forks, ND: 90°F
Aberdeen, SD: 93°F
Pierre, SD: 95°F
*Broken Bow, NE: 98°F
*Grand Island, NE: 97°F
Lincoln, NE: 94°F
**Colorado Springs, CO: 87°F
(asterisk = October record broken;
double asterisk = October record tied)

The poster child for this autumn heat wave may be Fargo, ND, where the high on Sunday, October 11, was 97°F. Not only was it Fargo’s hottest day of 2015 thus far, but it was by far the warmest temperature ever observed so late in the year. Nothing so toasty had ever been recorded in Fargo any later than September 22, when the city soared to 101°F in 1936. Even in midsummer, hitting 97°F isn’t all that common in Fargo: from 1990 to 2014, that mark was reached in only 7 of 25 years.

Further south, the readings were less anomalous, but still hot enough to break records and break out summertime garb. Wichita Falls, TX, simmered with a daily record high of 97°F, and San Diego, CA, basked in record daily warmth of 94°F. The warmth in California was also aided by downslope winds, but in this case heading the other direction--blowing offshore from east to west, around the south side of the sprawling zone of high pressure covering the U.S. West. Such patterns often give California its warmest temperatures of the year, along with enhanced wildfire risk. Camarillo, CA, set an all-time high of 108°F on Friday, October 9, breaking the mark of 103°F set on September 24, 1978.

Not to be outdone, parts of south-central Canada got in on the warmth, which added a balmy touch to the Thanksgiving weekend. (Canada’s Thanksgiving is celebrated each year on what’s commonly known in the U.S. as Columbus Day and recognized as Indigenous Peoples' Day at a number of U.S. locations). Saskatoon, Saskatchewan, hit 78°F on Saturday, compared to the daily record of 80°F and an average high of around 54°F. Winnipeg, Manitoba, made it to 75°F on Sunday, falling short of the daily record of 79°F but still more than 20°F above average. High winds were blasting the Northern Plains on Monday behind a sharp cool front ushering in more seasonable air. Wind gusts could reach 120 km/hr (75 mph) in parts of the Winnipeg area, according to Environment Canada. High wind warnings are in effect for eastern ND and SD and western MN; winds gusted to 59 mph at Cooperstown, ND, on Monday morning.


Figure 2. State-by-state ranking of average temperatures observed in September for the contiguous United States. Image credit: NOAA National Centers for Environmental Information.

Second-warmest September in U.S. weather records
With a 48-state average that came in 3.7°F above the 20th-century average, last month was the second-warmest September for the contiguous U.S. in 121 years of record-keeping, topped only by September 1998. A set of nine widely dispersed states had their warmest September on record: Connecticut, Colorado, Maine, Michigan, Minnesota, New Mexico, Rhode Island, Utah, and Wisconsin. The month was also on the dry side, coming in as the 21st-driest September of the past 121 years.

For the year to date, the 48-state average is eighth warmest on record, although that obscures record Jan-Sep warmth in four states (California, Oregon, Washington, and Nevada) and below-average readings from the mid-Mississippi Valley to New England.


Figure 3. Comparison of first-freeze climatology (1981-present) with conditions to date at first-order observations stations across the United States. Colored areas on map show the average date of the first freeze. The circles show whether each location has had a freeze (large purple) or no freeze yet (small gray). Image credit: Brian Brettschneider, @Climatologist49.


Figure 4. A view toward Centennial Ridges Trail in southeast Canada’s Algonquin Park (about 150 miles northeast of Toronto) on October 7, 2015. Sugar maples in the park hit peak on October 3 this year. Since 1975, the peak date has ranged from as early as September 15, 1982, to as late as October 9, 1996. Image credit: Algonquin Provincial Park.

The widespread warmth of September has delayed the first frost across many parts of the northern U.S. and the first snow over much of the Rockies. Most of South Dakota and western Nebraska normally get their first freeze by the end of September but have yet to touch 32°F this year (see Figure 3 above). The legendary fall foliage of New England has also taken a hit, as the color change is at least a week later than average in some locations--enough to compromise leaf-peeping for those who scheduled short trips well in advance. Yankee magazine’s live fall foliage map on Monday showed only a small part of northernmost New York and northern Vermont at peak color, with most of northern New England now in the “moderate” category. Northernmost Maine is also now near peak, according to the state’s official foliage website. By contrast, Yankee’s interactive map of average conditions shows that northern New England is usually at or past peak by this point, with the current conditions more comparable to those found on average during the last week of September.

The foliage-hastening effects of decreasing sunlight should begin to outweigh the warmth-induced delay as October proceeds. Temperatures this month over northern New England are running a bit below average, which should also help get the fall foliage spectacle rolling.


Figure 5. MODIS image of Tropical Storm Nora to the southeast of Hawaii's Big Island as seen from NASA's Aqua satellite on Sunday, October 11, 2015. At the time, Nora was at peak strength with top winds of 70 mph. Image credit: NASA.

Action in the Pacific: Tropical Storm Nora, 96E, 91W, and 92W
Earth's only active tropical cyclone on Monday was Tropical Storm Nora, which is expected to turn north on Tuesday east of Hawaii, missing the islands by over 500 miles. Steadily increasing wind shear should reduce Nora to a remnant low by Thursday.

Our three top models for predicting tropical cyclone genesis predict that an area of disturbed weather located at 8 am EDT Monday about 675 miles south of Manzanillo, Mexico (Invest 96E) will develop into a tropical depression late this week. This system is expected to move westwards at 10 - 15 mph and eventually turn north well east of Hawaii. Satellite loops show that 96E has an impressive amount of spin, but very few heavy thunderstorms. In their 8 am EDT Monday Tropical Weather Outlook, NHC gave 96E 2-day and 5-day odds of development of 10% and 80%, respectively.

Two tropical disturbances in the Western Pacific are forecast by the GFS and European models to develop into tropical depressions later this week: Invest 91W and Invest 92W. 91W was near Guam in the U.S. Mariana Islands on Monday, and is likely to move west to west-northwest this week, reaching a position a few hundred miles east of the Philippines' Luzon Island by the weekend. This storm will likely be the larger and more dangerous of the two systems. 92W will move west-northwest and pass through the northern Mariana Islands on Friday and Saturday.

Nothing cooking in the Atlantic
None of our reliable models for forecasting tropical cyclone development are predicting development of anything in the Atlantic over the next five days. There should be an increase in heavy thunderstorm activity over the Western Caribbean this weekend and early next week that will be worth watching for tropical cyclone development, though.

Bob Henson (temperatures), Jeff Masters (tropical)






Extreme Weather Heat Hurricane

Deadly Worldwide Coral Bleaching Episode Underway--Earth's 3rd on Record

By: Bob Henson , 12:47 PM GMT on October 09, 2015

Earth is entering its third worldwide coral bleaching event of the last 20 years--a disturbing example of how a warming planet can harm vital ecosystems--NOAA announced on Thursday. NOAA also released an eight-month outlook that projects even more bleaching to come in 2016. The only other global-scale bleachings in the modern era of observations happened in 1998 and 2010. Global bleaching is defined as an event that causes bleaching in each of the planet’s major coral-reef areas. "We may be looking at losing somewhere in the range of 10 to 20 percent of the coral reefs this year," NOAA coral reef watch coordinator Mark Eakin said, in an interview with Associated Press. Florida started getting hit in August. The middle Florida Keys aren't too bad, but in southeast Florida, bleaching has combined with disease to kill corals, Eakin said. It has also hit Cuba, Haiti and the Dominican Republic and is about to hit Puerto Rico and the Virgin Islands, he said, adding, "you kill coral, you destroy reefs, you don't have a place for the fish to live."

The current global bleaching is the culmination of regional problems that began in mid-2014, when very warm conditions emerged in several parts of the tropics. Hawaii is one of those areas: as Jeff Masters reported in July, Hawaii experienced its worst bleaching on record in 2014 when record-warm ocean temperatures caused 50 - 70% of the corals sampled in Northeast Oahu's Kāneʻohe Bay to bleach. Another hard-hit area was the coral-rich Papahānaumokuākea Marine National Monument, which extends hundred of miles northwest of the main Hawaiian Islands. “Last year’s bleaching at Lisianski Atoll was the worst our scientists have seen,” said Randy Kosaki, NOAA’s deputy superintendent for the monument. “Almost one and a half square miles of reef bleached last year and are now completely dead.” This year, the same warm waters that have fed record numbers of tropical storms and hurricanes have laid the foundation for additional bleaching in and near Hawaii. "Hawaii is getting hit with the worst coral bleaching they have ever seen, right now," Eakin said. "It's severe. It's extensive. And it's on all the islands." In one part of northwestern Hawaii, "the reef just completely bleached and all of the coral is dead and covered with scuzzy algae."


Figure 1. NOAA's four-month bleaching outlook (top) shows a threat of bleaching continuing in the Caribbean, Hawaii and Kiribati, and potentially expanding into the Republic of the Marshall Islands. An extended bleaching outlook (bottom) showing the threat of bleaching expected in Kiribati, Galapagos Islands, the South Pacific, especially east of the dateline. The bleaching may affect Polynesia and most coral reef regions in the Indian Ocean by May 2016. Corals experiencing "Alert Level 2" conditions (dark red colors) can expect widespread mortality due to severe bleaching. Image credit: NOAA.


Figure 2. Healthy corals play host to microscopic algae (zooxanethellae) that live in their tissues (panel 1). The coral reef helps protect the algae and provides the plants with carbon dioxide and key nutrients. At the same time, the algae serve as food for the coral and are the source of coral reefs’ often-spectacular colors. During stressful conditions (panel 2), algae leave the coral tissue. If the stress continues for weeks to months, the food-deprived corals experience bleaching: they lose their color and become more susceptible to disease or death (panel 3). Image credit: NOAA.


El Niño isn’t helping
Rising global temperatures are increasing the likelihood of bleaching, but it is often El Niño that pulls the trigger for the most widespread events. A strong El Niño can suppress upwelling and raise sea-surface temperatures across much of the central and eastern tropical Pacific and other low-latitude areas. Because the algae embedded in coral depend on photosynthesis to survive, coral reefs are limited to the uppermost reaches of the ocean, where sunlight can filter through. When the sea surface temperature is 1°C warmer than the highest monthly mean temperature corals usually experience, coral polyps will expel the symbiotic algae that live in their tissues, exposing the white skeleton underneath and resulting in a "bleached" appearance. Death can result if the stress is high and long-lived--for instance, if unusually warm ocean temperatures persist for months.


Figure 3. Divers laid out transect lines to guide surveys that took place in the coral reef habitats of American Samoa and the Pacific Remote Islands Marine National Monument from January to May 2015. Image credit: NOAA.


We may see major areas of bleaching in 2016 well beyond the period covered in the latest NOAA announcement. It is looking increasingly possible that a significant La Niña event will occur later in 2016 in the wake of the current El Niño event (see below). A recent study led by Joanie Klepyas (National Center for Atmospheric Research) examined heat stress in the Coral Triangle of the tropical Northwest Pacific. This is one of the world’s most expansive regions of coral reefs with nearly 600 varieties of coral and more than 2000 species of reef fish. Thanks to El Niño, much of the Coral Triangle is now experiencing sea-surface temperatures a bit below average, but the SSTs could rise quickly if El Niño segues into a moderate to strong La Niña. In 1998, this sequence of events led to the region’s worst bleaching event on record.

“I'm very concerned about the probability of intense bleaching in the Coral Triangle into 2016. NOAA's projections look a lot like what happened in the 1997-98 El Niño,” Kleypas told me in an email. “It is quite possible that the Coral Triangle region will experience warming later into 2016, even into the fall.”

When bleaching occurs year after year
Coral reef experts have warned that multi-year bleaching events could become increasingly common as our climate continues to warm in the 21st century. The possibility of two or more consecutive years of bleaching in Hawaii may be a harbinger of this future. Bleaching occurred from 2010 to 2013 in the Arabian/Persian Gulf, following widespread coral disease unrelated to bleaching in 2009. This was the first time four consecutive years of mass mortality have been observed in any coral reef on Earth. In a study published this spring, Bernhard Riegl and Sam Purkis (National Coral Reef Institute) took a close look at this four-year disaster and found what they call a “degradation cascade.” About two-thirds of the coral cover in the area studied was lost during the four-year event. Disease outbreaks often followed bleaching, and the corals that survived tended to shrink. “Certain coral species are more vulnerable to warming and disease than others, and as conditions degrade, one can expect to see big shifts in the coral communities,” noted Kleypas.

Disease fostered by warmer temperatures is a major threat to coral reefs in its own right, as explored in a 2015 study led by Jeffrey Maynard (Cornell University). “There is great spatial variation in the projected timing of the disease-favoring conditions, which is in keeping with much new research highlighting that the impacts of climate change will not be spatially uniform,” said Maynard and colleagues in the paper.

NOAA’s El Niño report for October
The well-publicized El Niño event of late 2015 continues to unfold pretty much as expected, according to the latest NOAA monthly diagnostic discussion. The latest probabilistic forecast issued by NOAA in conjunction with the International Research Institute for Climate and Society shows a greater than 95% chance of El Niño conditions persisting through the period Dec-Feb 2015-16, with a greater than 70% chance through March-May 2016. By the end of the period (May-July 2016), neutral conditions are the most likely outcome (just over 50%), although the odds of La Niña are beginning to rise quickly by that point. Major El Niño events are often but not always followed by a significant La Niña during the subsequent northern fall and winter.


Figure 4. Maximum temperatures for the week ending on October 6, 2015, soared above 36°C (96.8°F) across roughly half of Australia, with the heat especially intense for this time of year across southern parts of the continent. Image credit: Australia Bureau of Meteorology.

We can expect an increasing onslaught of El Niño signs and symptoms to emerge in the coming months. Across parts of Australia, vicious summer heat has arrived prematurely. Dozens of stations across southern Australia notched records over the last few days for their hottest day so early in the warm season. On October 5, the nation’s capital, Canberra, hit 31.8°C (89.2°F), the city’s earliest 30°C reading on record. Melbourne scored its earliest 35°C day ever recorded when it hit 35.8°C (96.4°F) on October 6. This hot spell follows the third-driest September in 106 years of Australian record-keeping. Extreme heat is a common byproduct of El Niño in the populous southeast part of Australia, as noted by the Bureau of Meteorology in a special statement on the October heat wave.

On a quirkier note, tuna crabs (pleuroncodes planipes) were reported on the beaches of Monterey Bay this week, far from their usual domain around Baja California. Their last sighting in Monterey was during the super-strong El Niño of 1982-83.

Have a great weekend, everyone! We'll be back with a new post on Monday at the latest.

Bob Henson

Heat Climate Change

Ex-Hurricane Oho Going Where Few Hurricanes Have Gone Before: Alaska

By: Jeff Masters , 3:45 PM GMT on October 08, 2015

Alaska and British Columbia are on alert to receive a very unusual dose of tropical weather: the remains of Hurricane Oho, which are on track to hurtle into the Alaska Panhandle on Friday evening. Oho completed the transition from a hurricane to an extratropical storm with 70 mph winds on Thursday morning, and after short period of weakening, is expected to interact with a powerful jet stream over the Gulf of Alaska and intensify on Friday afternoon off the coast of Alaska into a powerful 960 mb low pressure system with near-hurricane-force winds and heavy rain. A High Wind Warning is up for Sitka, Alaska for sustained winds of 40 to 55 mph with gusts of 65 to 75 mph on Friday. Sustained winds of 70 mph--just below hurricane-force--accompanied by 26-foot seas are expected over the offshore waters of the Alaska Panhandle from Cape Decision to Clarence Strait. The Juneau, Alaska NWS discussion from Thursday morning noted that 2 - 4" of rain is expected on Friday from the unusual storm, and "the dry week we just had has allowed rivers to fall...but risk of mudslides cannot be ruled out due to the extreme/unusual nature of this system."


Figure 1. MODIS image of Hurricane Oho as seen from NASA's Aqua satellite on Wednesday, October 7, 2015. At the time, Oho was a Category 2 storm with 105 mph winds. Image credit: NASA.

Hurricane Oho goes where few hurricanes have gone before
This is the second year in a row for the extratropical remains of a Central Pacific hurricane to affect the northwestern coast of North America. As I blogged about last year, Hurricane Ana, which took an extended tour of the Hawaiian Islands, then turned northeast and maintained hurricane strength to a latitude of 36.3°N--approximately the latitude of Monterey, California--transitioned to a powerful extratropical storm that brought strong winds and heavy rain to the Pacific Northwest and British Columbia on October 28, 2014. Only one other time since 1949 have the remains of a Central Pacific hurricane directly impacted the northwest coast of North American--when the extratropical remains of an unnamed 1975 storm that maintained hurricane strength remarkably far north, to 46.8°N (the latitude of the Oregon/Washington border), hit the region.

What's going on? Well, record-warm sea surface temperatures near the Hawaiian Islands the past two years have helped fuel highly unusual tropical cyclone activity in the waters surrounding the islands. The warmest water temperatures surrounding Hawaii are usually just below the threshold where a tropical cyclone can form and maintain itself, 26°C (79°F.) Water temperatures in these waters have been 27 - 28°C in much of the summer of 2014 and 2015, and that extra bump in temperature has pushed the Central Pacific past a threshold which allows more tropical storms and hurricane to form. (Note: it is more complicated that just a simple temperature influence, since low wind shear is also needed to increase tropical cyclone activity; however, the increased ocean temperatures have helped create a feedback in which wind shear has been lower over the Central Pacific in 2015.) In 2014, a record three hurricanes--Iselle, Julio, and Ana--came within 300 miles of the Hawaiian Islands, and two of these storms--Julio and Ana--tracked far to the north of the islands, where very few tropical cyclones have ever been observed. In September 2015, Hurricane Ignacio joined the club, penetrating to 32.4°N latitude as a hurricane, and 34.8°N as a tropical storm. Hurricane Oho maintained Category 2 strength on Thursday over a region of ocean well to the northeast of Hawaii where no hurricane that strong had ever been observed (Figure 2.) Since 1949, just ten Central Pacific tropical cyclones have pushed north of 34°N, and four of those storms occurred in 2014 and 2015--and latest model runs point to the possibility of a fifth storm joining the club, tropical disturbance Invest 95E, which is organizing in the waters to the east of Hawaii today.


Figure 2. Tracks of the ten Central Pacific tropical depressions, tropical storms, and hurricanes since 1949 to make it far to the north of the Hawaiian Islands (at least 34°N latitude.) An unusual number of these storms have occurred in the past two years--four out of the ten storms. Another one--currently dubbed Invest 95E--could join the club next week. Image credit: NOAA.

Next member of the Far-North-of-Hawaii Club: Eastern Pacific disturbance 95E?
The far-north of Hawaii hurricane club may get a new member next week: an area of disturbed weather in the Eastern Pacific located about 1350 miles southwest of the southern tip of the Baja California Peninsula (Invest 95E) that has the potential to develop into a tropical depression this weekend. Satellite loops show 95E has a modest amount of spin and heavy thunderstorms, and is slowly growing more organized. Our top three models for predicting tropical cyclone genesis all develop the system, and in their 8 am EDT Thursday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 40% and 70%, respectively. Models show 95E taking a west to west-northwest track over the next week, then turning northwards and missing Hawaii by at least 500 miles late next week.

Climate change may increase the number of Hawaiian hurricanes
The amazingly active Hawaiian hurricane seasons of 2014 and 2015 could well be a harbinger of the future, as I discussed in a 2014 blog post, Climate Change May Increase the Number of Hawaiian Hurricanes. A 2013 modeling study published in Nature Climate Change, "Projected increase in tropical cyclones near Hawaii", found that global warming is expected to increase the incidence of tropical storms and hurricanes in Hawaii. Lead author Hiroyuki Murakami, from the International Pacific Research Center at the University of Hawaii at Manoa, commented in a press release accompanying the paper: "Historically, only every four years on average did a tropical cyclone come near Hawaii. Our projections for the end of this century show a two-to-three-fold increase for this region."

Joaquin dies
Hurricane Joaquin is no more. The storm has become an extratropical storm over the cold waters of the north central Atlantic, ending its ten-day rampage. At its peak at 00 UTC October 2, Joaquin stood just below Category 5 status, with 155 mph winds and a central pressure of 931 mb. By the time Joaquin's remnant reaches Portugal on Saturday, the ex-hurricane should have top winds of about 35 mph.

Jeff Masters

Hurricane

Last Known Position of the Missing Ship El Faro: the Eyewall of Category 3 Joaquin

By: Jeff Masters , 4:12 PM GMT on October 07, 2015

When the container ship El Faro left Jacksonville, Florida early on the morning of September 30, 2015, Tropical Storm Joaquin, with top winds of 70 mph, was located a few hundred miles northeast of the Central Bahama Islands. Joaquin was forecast to move west-southwest at 6 mph towards the islands and intensify into a Category 1 hurricane by the next morning. The Captain knew he was charting a course that would take him within 200 miles of what was expected to be a hurricane, in a region where he could reasonably expect to see sustained winds near 35 mph and seas of ten feet--and even worse conditions if the storm put on an unanticipated bout of rapid intensification. Joaquin did just that, growing into a Category 3 hurricane with 120 mph winds by 8 am EDT October 1. According to information shared with me by David Adams of Reuters, a marine positioning database showed the last position of the El Faro, at 7:56 am EDT on October 1, was 23.52°N, 74.02°W--right in the northwest eyewall of Joaquin. Somehow, the ship lost power while approaching Joaquin--perhaps a rogue wave hit the ship, disabling it--and without propulsion, the counter-clockwise flow of winds that spiraled into the center of the hurricane drew the ill-fated ship into Joaquin's eyewall. A ship without engine power is little match for a major hurricane, and survival in the water with 120 mph winds and 30+ foot waves is a formidable task. CNN reports that the Coast Guard will call off the search for the 33 missing people from the El Faro at 7 pm EDT Wednesday.


Figure 1. Surface wind speed of Hurricane Joaquin (in knots) at 8 am EDT October 1, 2015, as estimated by NOAA/RAMMB using data from the Hurricane Hunters. The last known position of the ship "El Faro" is plotted. This position was from 7:56 am EDT, just four minutes prior to the wind analysis shown. The ship was in the eyewall, just 40 miles to the northwest of the center, in a region where the winds were in excess of 80 knots (92 mph.) At this time, Joaquin was a Category 3 hurricane with peak sustained winds of 120 mph, and was moving west-southwest at 5 mph. Joaquin's radius of maximum winds (RMW) at this time was about 19 miles in a ring surrounding the center, with the peak winds observed in the southwest quadrant of the storm. Significant wave heights at the El Faro's location at this time were likely 20 - 30 feet, but would have grown higher as the hurricane pulled the ship into the radius of maximum winds.


Figure 2. Hurricane Joaquin as seen by the GOES-13 satellite at 8:15 am EDT October 1, 2015, 19 minutes after the El Faro's last known position in the northwest eyewall of the Category 3 hurricane. Image credit: NASA/GSFC.

Joaquin now a tropical storm
Joaquin has weakened to a tropical storm with 70 mph winds as it speeds northeastwards at 35 mph out to sea. By Wednesday night, Joaquin will evolve into a powerful extratropical storm, and will steadily weaken as it heads towards Europe. By the time Joaquin reaches Portugal on Saturday, the ex-hurricane should have top winds of about 40 mph.


Figure 3. Hurricane Joaquin as seen by the MODIS instrument on NASA'a Terra satellite at 11:05 am EDT October 6, 2015. At the time, Joaquin was a Category 1 storm with 80 mph winds. Image credit: NASA.

Nothing else cooking in the Atlantic
NHC is no longer generating forecast model output or giving any odds of development for the area of low pressure (Invest 91L) that was about 400 miles east of the Lesser Antilles Islands on Wednesday morning. Satellite loops show that 91L is very unimpressive, with no spin and some disorganized heavy thunderstorms. This disturbance will bring some heavy rain showers and gusty winds to the northern Lesser Antilles Islands on Thursday, but none of our reliable models for forecasting tropical cyclone development are predicting development of this system, or anything else in the Atlantic, over the next five days.


Figure 4. MODIS image of Hurricane Oho as seen from NASA's Terra satellite on Tuesday, October 6, 2015. At the time, Oho was a Category 1 storm with 85 mph winds. Image credit: NASA.

Hurricane Oho misses Hawaii
Category 2 Hurricane Oho was speeding north-northeast at 34 mph in the waters 645 miles east-northeast of Hilo, Hawaii at 11 am EDT Wednesday. Oho was over waters of 27°C (81°F) on Wednesday morning, which is about 2°C above average--the warmest temperatures ever observed in these waters. On Thursday afternoon, Oho is expected to cross 140°W longitude, leaving the Central Pacific Hurricane Center's area of responsibility and entering the National Hurricane Center's area of responsibility. Only one other tropical cyclone that formed in the Eastern or Central Pacific has done that since record keeping began in 1949--an unnamed 1975 storm that maintained hurricane strength to 46.8°N (the latitude of the Oregon/Washington border.) That storm was the only hurricane on record to make it farther to the northeast of Hawaii than 2014's Hurricane Ana, which maintained hurricane strength to a latitude of 36.3°N--approximately the latitude of Monterey, California. Ana died about 1,300 miles west of the California/Oregon border.


Figure 5. Typhoon Choi-wan as seen by the MODIS instrument on NASA'a Aqua satellite at 03:25 UTC October 6, 2015. At the time, Choi-wan was a Category 1 storm with 75 mph winds. Image credit: NASA.

Typhoon Choi-wan headed towards Russia and Northern Japan
In the Western Pacific, massive Tropical Storm Choi-wan has weakened to 70 mph winds after encountering cold water and high wind shear, and the storm is expected to die on Thursday over Russia's Kuril Islands near Northern Japan.

Jeff Masters

Hurricane

Why Did the ECMWF Forecast Joaquin So Well?

By: Bob Henson , 8:35 PM GMT on October 06, 2015

The post-mortems have begun on how well Hurricane Joaquin was predicted, and one of the key themes is why the flagship global model of the European Centre for Medium-Range Weather Forecasts (ECMWF) beat NOAA’s Global Forecast System (GFS) to the punch in forecasting that Joaquin would remain well offshore. On Wednesday, September 30, less than six days from a potential landfall, the ECMWF operational model was consistently keeping Joaquin offshore, even as the GFS and nearly all other models were bringing the hurricane into the U.S. East Coast. From late Wednesday into Thursday, the GFS and other models began to shift toward an offshore track for Joaquin, as the hurricane itself was still diving southwestward into the Bahamas. By Friday, there was virtually unanimous model agreement on the offshore track that proved accurate.


Figure 1. Satellite image of atmospheric water vapor, collected at 1915Z (3:15 pm EDT) Friday, October 2, 2015. By this point, models agreed that Hurricane Joaquin would be moving out to sea, even though it was located unnervingly close to the southeast United States and moisture from Joaquin was already flowing onto the U.S. East Coast. Image credit: NOAA/NESDIS.

The National Hurricane Center did an admirable job of threading the needle in its public forecasts. NHC’s “cone of uncertainty” gradually edged toward the U.S. coast during the middle of last week. On Wednesday, the midpoint of the cone reached the mid-Atlantic coast, and the center’s forecast discussions acknowledged that they were splitting the difference between the insistently offshore ECMWF and other model guidance. The cone then began shifting back eastward on Thursday--but again, quite gradually, since the NHC works to avoid back-and-forth, “windshield-wiper” swings in projected track that could exacerbate public confusion. (One limit to the cone as currently designed is that the width of the cone is based on average track errors in recent years, rather than the actual uncertainty for a given hurricane, so in a case like Joaquin one wouldn’t have realized from a glance at the cone that the leading models differed so starkly.)


Figure 2. Official forecast track and cones of uncertainty issued by the National Hurricane Center at (left to right) 5 am and 5 pm EDT Wednesday, September 30, and 5 am and 5 pm EDT Thursday, October 1. Image credit: NHC.

It will take in-depth analysis to fully understand why the ECMWF was the first of the leading operational models to consistently keep Joaquin offshore. In 2012, the ECMWF model gained fame for correctly leading the pack in the opposite direction, as it was the first to call for Hurricane/Superstorm Sandy to hook into the New Jersey coast rather than remaining offshore. The fact that the ECMWF caught on to Sandy’s future ahead of the GFS model gained wide attention, and last week’s repeat victory for the ECMWF hasn’t escaped notice. On Friday, the New York Times published a summary of the computational, staffing, and design challenges that have hindered U.S. medium-range modeling efforts as compared to Europe’s.

Before jumping to conclusions...

Here are a few important things to keep in mind when contemplating the Battle of the Models:

--The GFS and ECMWF are both used to predict a vast array of weather events. These models have to be robust and durable in handling all kinds of atmospheric conditions in all seasons. Hurricane forecasting is an important task, but not their sole focus. Other models have been developed specifically for hurricane prediction, such as the hurricane-oriented version of the Weather Research and Forecasting model (HWRF) and the NOAA Geophysical and Fluid Dynamics Laboratory (GFDL) hurricane model. In 2014, HWRF led all other individual models in 2- and 3-day track forecasts (see Figure 3). For track guidance beyond 3 days, forecasters tend to put the most weight on the GFS and ECMWF, along with the UK Met Office model (UKMET).


Figure 3. Skill of computer model forecasts of Atlantic named storms in 2014, compared to a "no skill" model called "CLIPER5" that uses just climatology and persistence to make a hurricane track forecast (persistence means that a storm will tend to keep going in the direction it's current going.) OFCL=Official NHC forecast; GFS=Global Forecast System model; GFDL=Geophysical Fluid Dynamic Laboratory model; HWRF=Hurricane Weather Research Forecasting model; ECMWF=European Center for Medium Range Weather Forecasting model; UKMET=United Kingdom Met Office model; TVCA=one of the consensus models that blends together up to five of the above models; CMC=Canadian Meteorological Center (GEM) model; BAMM=Beta Advection Model (Medium depth). Data taken from the National Hurricane Center 2014 verification report.


--Individual high-profile events like Sandy and Joaquin can obscure the big picture. As Jeff Masters reported last week (scroll article to “Which track model should you trust?”, the ECMWF and GFS were virtually tied as the best-performing models for hurricane tracking when averaged over the period 2011-2014. As a guiding rule, the best forecasts emerge from a consensus that include a wide variety of models, rather than by going solely with the ECMWF or any other single model. This is why the NHC track forecasts lean heavily toward multi-model consensus, as was the case last week. Official NHC track predictions are often very close to the output from a model blend called TVCA, which employs the five models mentioned above (ECMWF, UKMET, GFS, GFDL, and HWRF). See our roundup post from August on recent improvements to the GFS and ECMWF as well as other leading models used for hurricane prediction.

--Overall the GFS and ECMWF are both very capable, sophisticated global models, and both are continually being revised and improved. Multiyear analyses tend to give the ECMWF a slight edge in overall performance across the range of weather features predicted. On average, the GFS lags the ECMWF model by about half a day in predicting upper-level weather features (i.e. centers of high and low pressure at the 500-millibar level, about 4 miles high). That margin has remained more or less constant over the last decade as both models have improved. The GFS now predicts 500-mb features out to 8 days with the same level of skill as 5-day forecasts of the 1980s. “Both models are world class models. I think that often gets lost in the crossfire,” said Marshall Shepherd in a Forbes essay published on Friday.


Figure 4. The number of days of useful skill produced by various models beyond 6 days (top lines) and 8 days (bottom lines) in predicting the height of the 500-millibar surface, which translates into the location of the upper-level highs and lows that shape surface weather. In recent years, the ECMWF has provided about 14.5 days of measurable skill, while the GFS has provided about 14 days. Image credit: NOAA/NWS Environmental Modeling Center, from “Improvements in Forecast Skill of the NCEP Production Suite,” Glenn White et al., presented in June 2015 at the 27th AMS Conference on Weather Anlysis and Forecasting.


--The ECMWF was created by 18 European nations in the 1970s with a very specific mission: “to pool Europe's meteorological resources to produce accurate climate data and medium-range forecasts.” A typical definition of “medium-range” is the period from 3 to 7 days, although ECMWF now produces a variety of forecast products out to 10 days and beyond. NOAA, in contrast, issues a much larger variety of forecasts and other products for a larger, more diverse customer base. The short-term High-Resolution Rapid Refresh (HRRR) model is one example of a recent NOAA innovation that falls outside the bailiwick of ECMWF. NOAA’s huge array of responsibilities limits the amount of resources it can devote to global forecast systems like the GFS, especially in an era with relentless pressure on U.S. science budgets. In the aftermath of Sandy, NOAA did receive supplemental funding that allowed for major progress, including a doubling of GFS horizontal resolution, implemented in January 2015, and a tenfold increase in supercomputing capacity being implemented this year. At the same time, ECMWF continues to upgrade its own models and computing resources, so the race continues.

One current weakness in the GFS relative to the ECMWF, noted in the New York Times article, is its technique for data assimilation (bringing as many observations as possible into the starting point of a model run). ECMWF employs a four-dimensional data assimilation technique, while the GFS uses a 3D technique. The fourth dimension is time: the 4D system allows data from satellites and other sensors to be woven into a model run over multiple time steps, rather than being injected into the model at a single time step. In this and several other ways, including the ability to draw on a wider range of observations, the ECMWF data assimilation appears to give it the edge. A 4D data assimilation system is now being developed for the GFS, perhaps to be incorporated within the next year.

Did cumulus clouds make the difference in Joaquin’s track forecasts?
Looking back at Hurricane Sandy, some interesting research led by Nicholas Bassill (University at Albany, State University of New York) points to one explanation for the ECMWF’s triumph with that storm: the way in which the model depicted (or parameterized) cumulus clouds that were too small to be modeled directly. Bassill found that when the WRF-ARW model was run using the ECMWF’s cumulus parameterization technique, it performed similarly to the ECMWF in bringing Sandy onshore. However, when the WRF-ARW was run with the GFS cumulus parameterization, it kept Sandy offshore (see Figure 5).

The GFS parameterizations have undergone some upgrades since 2012, and we can’t immediately tell for sure if this difference in cumulus treatment mattered in the case of Joaquin. Bassill does think that large-scale latent heat release within cumulus clouds (the energy released when water vapor condenses to form cloud droplets and raindrops) probably altered the evolution of important features upstream of the upper-level trough northeast of Joaquin that helped steer it away from shore. Also, he told me, “perhaps the ECMWF was better at assimilating satellite winds in the area to better capture this feature. You'd need further study to definitively say.”

Bob Henson


Figure 5. Results from nine 7-day forecasts extending from 1200 GMT October 23 to October 30, 2012, showing the variety of solutions for Hurricane Sandy that were obtained in research mode by running the same model (WRF-ARW) nine times. The only difference between each run is the method used for cumulus parameterization (handling the cumulus clouds that are too small to be directly simulated within the model). The parameterization techniques used for the NAM and GFS models led to an offshore track, whereas the technique used in the ECMWF model brought Sandy onto the northeast U.S. coast. Image credit: Nick Bassill.

Hurricane

Carolina Floods Breach 18 Dams and Kill 16 People; Tropics Quiet Down

By: Jeff Masters , 3:16 PM GMT on October 06, 2015

South Carolina and North Carolina's epic deluge has finally ended after five days of ceaseless rains. No rain is expected to fall in either state through Thursday, giving time for the swollen rivers to recede and flooded communities to recover. The storm has killed at least fourteen people in South Carolina (eight drownings and six traffic deaths); an additional two storm-related fatalities were reported in North Carolina. The peak 5-day rainfall amount from the storm was 27.15", at CoCoRaHS station SC-CR-69 in Mount Pleasant, a suburb of Charleston on the city's northeast side. As of 9 am EDT Tuesday, 306 state-maintained roads and 163 bridges were closed in South Carolina, which was down from a high of 368 roads/171 bridges closed at 10 pm EDT Monday. The South Carolina Emergency Management Division tweeted Tuesday morning that eighteen dams had been breached statewide.

The National Weather Service Facebook page has an excellent animation showing the evolution of Joaquin and then the low pressure system that brought the heavy rains to South Carolina.


Figure 1. A church is surrounded by flood waters on October 5, 2015 in Columbia, South Carolina. Image credit: Sean Rayford/Getty Images.

Hurricane Joaquin speeding out to sea
Hurricane Joaquin is still a Category 1 hurricane as it speeds northeastwards out to sea, but the storm will not affect any more land areas as a tropical cyclone. By Wednesday night, Joaquin will evolve into a powerful extratropical storm, and will likely bring strong winds and heavy rain to Europe this weekend.

The Miami Herald has an excellent series of images showing the path of the ill-fated El Faro into Hurricane Joaquin, with the NHC advisory cones superimposed. It sure looks like forecast uncertainty should not have contributed much to the loss of the vessel and the 33 crew members on board.

91L approaching Lesser Antilles with no signs of development
An area of low pressure (Invest 91L) centered at 8 am EDT Tuesday about 850 miles east of the Lesser Antilles Islands is moving west-northwest at 15 - 20 mph. Satellite loops show that 91L is very unimpressive, with little spin or much in the way of heavy thunderstorms. Wind shear is currently high, 30 - 35 knots, but will drop to the moderate range, 10 - 20 knots, by Thursday, according to the 8 am EDT Tuesday run of the SHIPS model. One of our three reliable models for forecasting tropical cyclone genesis, the European model, shows some development of 91L this weekend, after the storm turns north over the open Atlantic. 91L may bring some heavy rain showers and gusty winds to the northern Lesser Antilles Islands on Thursday. 91L will turn to the north on Friday, and is not likely not affect any other land areas. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 0% and 20%, respectively.


Figure 2. MODIS image of Tropical Storm Oho as seen from NASA's Aqua satellite on Monday, October 5, 2015. At the time, Oho had winds of 65 mph. Image credit: NASA.

Hurricane Oho skirting Hawaii
In the Central Pacific, Hurricane Oho is churning the waters about 300 miles south-southeast of the Big Island of Hawaii; Oho was upgraded to a hurricane at 11 am EDT Tuesday, becoming the seventh hurricane of the 2015 season in the North Central Pacific. Oho is headed east-northeast away from Hawaii, and is not expected to bring strong winds or heavy rain to the state; high surf will be the main impact of the storm felt in the islands. In their 11 am Tuesday Wind Probability Forecast, the Central Pacific Hurricane Center gave no odds that any point in Hawaii would receive tropical storm-force winds.

Typhoon Choi-wan headed towards Northern Japan
In the Western Pacific, massive Typhoon Choi-wan has intensified into a Category 1 storm with 80 mph winds, and is expected affect Northern Japan as a strong tropical storm on Thursday.

Bob Henson will have a post this afternoon discussing the excellent performance of the European model for Hurricane Joaquin.

Jeff Masters

Flood Hurricane

More than Two Feet of Rain in South Carolina; Joaquin Heads to Sea

By: Bob Henson and Jeff Masters , 5:45 PM GMT on October 05, 2015

The end is finally in sight for the epic multi-day rains that have pummeled the Carolinas over the last five days. Areas through the triangle from Columbia to Charleston to Myrtle Beach were especially hard-hit this weekend (see Figure 2). At least 9 flood-related deaths were reported across the Carolinas by Monday morning, and countless homes and cars were flooded. Transportation tangles continue across the region. As of 10 am EDT Monday, the flood had closed 391 roads and 165 bridges across South Carolina, according to the state’s department of transportation. This includes more than 70 miles of Interstate 26. Persistent high tides and coastal flooding have led to additional road closures in Virginia and Delaware. Highway 12, the main road connecting the Outer Banks, is closed in both directions at two points, near Ocracoke and Kitty Hawk, with reopening expected by 5 pm EDT Tuesday.

The upper low responsible for the epic rains is finally pushing offshore into the Atlantic, but extensive wrap-around rainbands continue across southeast North Carolina, with more widely scattered showers and storms across South Carolina. Short-range models hint that today could bring a final dose of rain totaling more than 1” in spots along a swath from near Columbia, SC, to Hatteras, NC.


Figure 1. A vehicle and a home are swamped with floodwater from nearby Black Creek in Florence, S.C., Monday, Oct. 5, 2015 as flooding continues throughout the state following several days of rain. Image credit: AP Photo/Gerry Broome.


Figure 2. 7-day rainfall totals for the period from 12Z (8:00 am EDT) Monday, September 28, through Monday, October 5, 2015. Observations are analyzed on a 4 km by 4 km grid using data from raingauges and NWS/NEXRAD radar, with supplementation by satellite data as needed. Image credit: NWS/NOAA Advanced Hydrologic Prediction Service.

How the numbers are stacking up
The heaviest 24-hour rainfall at downtown Charleston happened to fall from midnight Friday night to midnight Saturday night: 9.25”. This total fell short of the record for any 24-hour period, which remains 10.57” on Sept. 6-7, 1933. (The calendar-day record also stands: 10.38” on June 11, 1973.) WIth nearly nearly four weeks left in October, Charleston may yet approach its jaw-dropping monthly record of 27.24”, set in June 1973. According to WU weather historian Chris Burt, Charleston has the longest period of record for precipitation observations in the United States. Although the record is discontinuous, rain/snow observations began almost 300 years ago in Charleston. They extend from 1738 to the present (including the entire Civil War) except for the periods 1766-1784, 1792-1806, and 1812-1831.

The rains weren’t quite as heavy at the official reporting station in Columbia, but they managed to give the city its wettest calendar day on record: 6.87” on Oct. 4, 2015 (old record 5.79” on Jul. 9, 1959). Columbia also notched its wettest two-day period on record: 10.44” on Oct. 4-5, 2015 (old record 7.69” on Aug. 16-17, 1949).

From the Columbia area east to Georgetown, several Weather Underground PWSs have racked up impressive totals, consistent with Figure 1 above.



Nick Wiltgen (The Weather Channel), who compiled a large amount of rainfall data from the region, notes that these totals appear to have clearly smashed the previous state record for 5-day precipitation, which had been 17.44” in downtown Greenville (Aug. 22-26, 1908). We’ll have to wait till Tuesday to see which station ends up on top, since any additional rain today will further boost the 5-day totals for October 1-5. A number of CoCoRaHS stations have racked up especially high storm totals, including the following (courtesy Dr. Greg Forbes, The Weather Channel):

26.88" - 6 NE Mount Pleasant, Charleston Co SC
25.50" - 3 SE Cainhoy, Charleston Co SC
24.75" - Kingstree, Williamsburg Co SC
24.10" - 3 SSW Shadowmoss, Charleston Co SC
23.74" - Longs, Horry Co SC
23.61" - 5 SSE Charleston SC
23.46" - 10 NW Kingstree, Williamsburg Co SC
22.02" - 1 NNW Limerick, Berkeley Co SC
21.45" - 3 SW Folly Beach, Charleston Co SC
20.75" - Millwood, Sumter Co SC
20.42" - 4 E Moncks Corner, Berkeley Co SC
20.28" - Gills Creek (Columbia), Richland Co SC

See also this link (not a permalink) to the latest public information statement from the National Weather Service office in Charleston, which includes many of the reports above. State and national climatologists would need to carry out further analysis to verify the accuracy of any weather station and confirm the validity of its reports before new champions are confirmed.

More than a thousand-year rain?
Using about a century of precipitation records, NOAA has constructed a Precipitation Frequency Data Server, which estimates how often we might expect to see extreme rainfall events recur. From this database, the three-day 1-in-1000 year rainfall amounts for Charleston and Columbia are 17.1" and 14.2", respectively. The 24-hour 1-in-1000 year rainfall amounts for Charleston and Columbia are 14.8", and 12.5", respectively. (Hydrologists would refer to a 1-in-1000-year rain as having a typical "recurrence interval" of 1000 years. The idea is that such events are not always separated by 1000 years; the same amount of rain could conceivably occur the very next year, or might not occur until thousands of years later.) Comparing these numbers to the data above, it appears that the one-day event may not have reached the 1000-year recurrence mark, but the 3- to 5-day cumulative totals of more than 20” easily exceeded it (see Figure 3 below). These totals actually suggest a recurrence interval well beyond 1000 years, but the NOAA database does not extend to longer time periods, in part because it becomes progressively more difficult to estimate the intervals as they become longer. Note that these recurrence interval calculations assume the climate isn't changing, which is incorrect. Global warming puts more moisture into the atmosphere, shifting the odds of extreme rainfall events like this to be considerably more likely.


Figure 3. Recurrence-interval curves for the area near Sumter, SC, as calculated by NOAA’s Precipitation Frequency Data Server. These estimates are based on NOAA’s Atlas 14 calculation of the expected recurrence frequency of rainfall events for various amounts and time periods. Across much of the northeast half of South Carolina, three-day amounts of 20” or more would easily top the 1000-year recurrence intervals. South Carolina’s data are based on the 2004 edition of Atlas 14, so they may not fully reflect the influence of recent climate change in boosting the likelihood of extremely heavy rain.


Averaged across the state as a whole, the wettest three calendar months in South Carolina weather history are July 1916 (14.41"), September 1924 (13.16"), and September 1928 (12.70"). All of these were related to tropical cyclones passing through or near the state. The last five days alone have already brought South Carolina close to the wettest month in state history--without a tropical cyclone landfall!

The Carolina rains are only the latest in a remarkable year of prolonged torrential rain events across parts of the United States. Texas and Oklahoma have already notched their wettest months on record (by far) this past May, and Illinois had its second-wettest month on record in June. Research has confirmed that our warming climate is making intense short-term rains (such as the highest 1-day totals) even heavier in many parts of the United States and the world, as warmer temperatures allow more moisture to evaporate from oceans and flow into rain-making storm systems. Less research has been done on trends in multi-day rainfall events, although the same general principle should apply. Just as warming temperatures are folded into the 30-year NOAA database used for calculating local average highs and lows, our increasing prevalence of extreme precipitation events can be expected to gradually shift the odds reflected in the recurrence intervals discussed above. It’s also possible that the ongoing El Niño event, which has intensified throughout 2015, has played a role in boosting the amount of water vapor available for heavy rains across the southern U.S. For more on the science of extremely heavy rainfall, see Bob Henson's May 2015 post, The Rains of May and the Science of Recurrence Intervals.

At Capitol Weather Gang, Jeff Halverson and colleagues have published an excellent first-cut analysis of the meteorology behind the Carolina rain event.


Figure 4. Satellite image Hurricane Joaquin (right) and the powerful low pressure system bringing heavy rain to the Southeast U.S. (left) taken at 9:15 am EDT October 5, 2015. At the time, the hurricane was a Category 1 storm with top winds of 85 mph. A band of very heavy rain can been seen feeding into South Carolina, to the west of the hurricane. Image credit: NOAA Visualization Laboratory.


Figure 5. Radar image of Hurricane Joaquin taken at 9:13 pm EDT October 4, 2015, from the Bermuda radar.

Hurricane Joaquin brushes Bermuda
Hurricane Joaquin passed 75 miles to the northwest of Bermuda on Sunday evening as a Category 2 storm with 100 mph winds, bringing tropical storm-force winds and heavy rain to the island. Bermuda International Airport reported sustained winds of 48 mph, gusting to 64 mph, at 1 am EDT Monday. Bermuda probably has the most hurricane-resistant infrastructure of anyplace on Earth, and I expect damage will be minimal on the island. Category 1 Joaquin is now speeding north-northeast out to sea, and will not affect any more land areas as a tropical cyclone. By Wednesday, Joaquin will evolve into a powerful extratropical storm, and will likely bring strong winds and heavy rain to Portugal this weekend.


Figure 6. Damage on Crooked Island in the Bahamas after Hurricane Joaquin as grabbed from a video posted to The Weather Channel.

Hurricane Joaquin heavily damages the Bahamas
Communications with the islands in the Bahamas most heavily damaged by Hurricane Joaquin are still tenuous, but it is clear that damage was heavy on Crooked Island, Acklins Island, Long Island and San Salvador. One death has been reported on Long Island due to high winds collapsing a home. The Coast Guard is still searching for survivors from the container ship El Faro, which is presumed to have gone down in the hurricane. One body from the crew of 33 has been recovered.

91L approaching Lesser Antilles with no signs of development
An area of low pressure (Invest 91L) centered at 8 am EDT Monday about 1000 miles east of the Lesser Antilles Islands is moving west-northwest at about 15 mph. Satellite loops show that 91L has a decent amount of spin, but almost no heavy thunderstorms. Wind shear is currently moderate, 10 - 15 knots, but will rise to the high range, 20 - 25 knots, on Tuesday and Wednesday, according to the 8 am EDT Monday run of the SHIPS model. One of our three reliable models for forecasting tropical cyclone genesis, the UKMET model, does develop 91L into a tropical depression late this week, as the storm heads northwards in the open Atlantic. 91L will bring heavy rain showers and gusty winds to the northern Lesser Antilles Islands beginning on Thursday morning. In their 8 am EDT Monday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 10% and 20%, respectively.

Tropical Storm Oho skirting Hawaii
In the Central Pacific, Tropical Storm Oho is churning the waters about 300 miles south of the Big Island of Hawaii. With wind shear expected to relax over the next few days, Oho has a chance to intensify from its current 50 mph winds to the threshold of Category 1 hurricane status, 70 mph winds, as it heads north-northeast to northeast. While the storm is not expected to threaten Hawaii, the Air Force Hurricane Hunters are scheduled to fly the storm Monday afternoon, and the NOAA jet will fly a dropsonde mission to aid in model forecasts for the storm. In their 11 am Wind Probability Forecast, the Central Pacific Hurricane Center was giving only one place in Hawaii odds of seeing tropical storm-force winds--South Point on the Big Island, with a 3% chance.

Tropical Storm Choi-wan headed towards Northern Japan
In the Western Pacific, Tropical Storm Choi-wan is expected to head northwards towards Northern Japan this week and potentially intensify into a Category 2 typhoon. Choi-wan will then likely weaken to a tropical storm before it reaches Northern Japan on Thursday.

Tornadoes from Typhoon Mujigae kill 6 in China
Category 4 Typhoon Mujigae made landfall on the north side of the city of Zhanjiang, China near 1 am EDT Sunday (05 UTC), with sustained winds of 130 mph. Several powerful tornadoes spawned by the typhoon killed at least six people (video and new story here.) Qingqing Li of the Pacific Typhoon Research Center, Nanjing University of Information Science and Technology, alerted me of these videos of the tornadoes as well:

http://video.weibo.com/show?fid=1034:bed4e4b67f0fd9a2396ca4564f38270a
http://video.weibo.com/show?fid=1034:eeb1fafeee6d502df3c947519469e728

Deadly flash flood hits the French Riviera
At least 19 people were killed as the much-visited southeast coast of France was struck by disastrous flash flooding along the French Riviera on Saturday night. Mediterranean resort towns beloved by jet-setting tourists, such as Cannes, Nice and Antibes, were devastated by the torrential weekend downpour, which trapped residents in cars, parking garages and retirement homes. Rivers of water gushed through some of the world's wealthiest streets, scattering cars hundreds of feet from where they were parked and destroying businesses in what were described as 'apocalyptic' scenes. After a river surged over its banks, three people were killed in a retirement home. In just one hour, Cannes received a record 107 mm (4.21”); the previous one-hour record was 70 mm (2.76”). Dew points surged into the lower 60s Fahrenheit on Saturday at Cannes. On Sunday, supercell thunderstorms tore across northern Italy as the front responsible for the French floods surged eastward.


Figure 7. Intense thunderstorms can be seen along the coast of the French Riviera in this infrared satellite image, collected at 1800 GMT (8:00 pm local time) on Saturday, October 3. Image credit: CIMMS/SSEC/University of Wisconsin.


Figure 8. A man walks past damaged cars, in Mandelieu-la-Napoule, southern France, on October 5, 2015 after floods tore through the French Riviera. Cars are often stacked in this manner in the aftermath of flash floods, as was the case during the catastrophic Rapid City, SD, flood of 1972 (scroll page for photo). (image credit: Rapid City Image credit: Anne-Christine Poujoulat/AFP/Getty Images.

Portlight disaster relief charity responding to South Carolina flooding
The South Carolina-based Portlight.org disaster relief charity, founded and staffed by members of the wunderground community, is responding to the devastating South Carolina floods by working with emergency management agencies to help ensure that those still stranded are brought to safety. They will be working with Red Cross shelters to ensure they're accessible to all, and as always, will be ready to replace lost or damaged medical equipment. If you're in South Carolina and you'd like to volunteer with them, please email the Operations Manager, Shari Myers, shari@portlight.org. You can follow Portlight's progress on the Portlight Blog. Please consider a donation to Portlight's disaster relief fund at the portlight.org website.

We'll have our next update on Tuesday.

Bob Henson (rainfall); Jeff Masters (tropical)


Hurricane Flood

Devastating Rains in South Carolina; Joaquin Lashing Bermuda

By: Bob Henson and Jeff Masters , 8:01 PM GMT on October 04, 2015

One of the most widespread and intense multi-day rain events in the history of the Southeast is bringing misery and destruction to thousands of residents. A broad swath of deep tropical moisture extending west from Hurricane Joaquin has intercepted a preexisting frontal zone and a strong upper-level low parked over the Southeast. These factors produced a NW-to-SE band of extremely heavy rain on Saturday from the northern South Carolina coast to the Uplands at the other end of the state. Flooding is widespread, and at least four deaths have been reported.

On Sunday, the band was slowly pivoting in counterclockwise fashion to a more W-to-E orientation. This was providing some relief to Charleston, which experienced a flash flood emergency with countless water rescues at high tide late Saturday night. The worst conditions on Sunday afternoon had shifted north to the area from Columbia to Myrtle Beach, where numerous flash flood watches and warnings were in effect. “The City of Georgetown is predominantly under water,” said Georgetown (SC) fire chief Joey Tanner, at 11:30 am EDT Sunday. Extensive coastal and tidal flooding has also returned to the Virginia and North Carolina coast, where an intensification of onshore flow has produced tides around 3 feet above normal on Sunday, comparable to those observed on Friday.


FIgure 1. An American Red Cross van was stranded in floodwaters on U.S. Hwy. 17 North near Georgetown, S.C., on Sunday, October 4, 2015. Several sections of Highway 17 were shut down between Charleston and Georgetown. Image credit: AP Photo/Mic Smith.


Figure 2. NWS/NEXRAD radar imagery at 2:50 pm EDT Sunday, October 4, 2015, showed a persistent swath of rain with very heavy embedded cells, extending from west to east across much of South Carolina and far south North Carolina. Image credit: WU’s Storm app for iPad.


Sunday’s is the second round of extremely heavy rain for the SC/NC border area, which was first hammered on Thursday and Friday. Conditions will gradually improve through most of the Carolinas tonight into Monday as the upper low begins to move eastward, but the coastal border area will be the last to see the heavy rain depart. From roughly Florence, SC, to Wilmington, NC, we may end up with some truly phenomenal 3- to 5-day rain totals. According to Dr. Greg Forbes of the Weather Channel, an NWS employee 3 miles northeast of Boone Hall Plantation in Charleston County reported a storm total of 24.23” on Sunday morning. It would not be surprising to see a number of storm totals in the 15” - 25” range, and perhaps several beyond 25”. We can also expect to see significant river flooding over the next several days as runoff from the inland rains makes its way downstream.

Here are several records already set in South Carolina:

--At the Charleston airport (CHS), 14.48” fell from Thursday through Saturday, October 1-3. This beats the previous 3-day record of 11.95” set on June 9-11, 1973. Most of the rain--11.50”--fell on Saturday, October 3, beating the previous calendar-day record of 10.52” (September 21, 1998). Weather records at CHS began in 1983.

--At Downtown Charleston, where weather records began in 1870, the total of 13.80” for October 1-3 beats the previous 3-day record of 12.39”, set on June 9-11, 1973.

--At Columbia, at least 7.46” had fallen on Sunday as of 2:00 pm EDT. Combined with 0.46” on Friday and 3.57” on Saturday, this gives Columbia an unofficial three-day total of at least 11.46”, with rain still falling.

Using about a century of precipitation records, NOAA has constructed a Precipitation Frequency Data Server, which estimates how often we might expect to see extreme rainfall events recur.  According to NOAA's Precipitation Frequency Data Server, these could be 1-in-1000 year rains for some locations. (Hydrologists would refer to a 1-in-1000-year rain as having a typical "recurrence interval" of 1000 years. The idea is that such events are not always separated by 1000 years; the same amount of rain could conceivably occur the very next year, or might not occur until thousands of years later.) The three-day 1-in-1000 year rainfall amounts for Charleston and Columbia are 17.1" and 14.2", respectively. The 24-hour 1-in-1000 year rainfall amounts for Charleston and Columbia are 14.8" and 12.5", respectively.


Figure 3. 24-hour recurrence intervals for rainfall from 8:00 am EDT Saturday, October 3, through Sunday, October 4. A large swath from Columbia to Charleston experienced 24-hour rainfalls that would be expected to recur less than once every 100 years. Recurrence intervals of greater than 100 years are not shown in this analysis. Multi-day rainfalls by the time this event is over may reach the 1-in-1000-year recurrence interval in some locations. MetStat computed the recurrence interval statistics based on gauge-adjusted radar precipitation and frequency estimates from NOAA Atlas 14 Volume 8, published in 2013 (http://dipper.nws.noaa.gov/hdsc/pfds/.)MetStat does not supply their precipitation recurrence interval forecasts or premium analysis products for free, but anyone can monitor the real-time analysis (observed) at: http://metstat.com/solutions/extreme-precipitation-index-analysis/ or on their Facebook page. Image credit: MetSTAT.


Adding insult to injury, the Southeast Regional Climate Center reported on Sunday that the Raleigh-Durham International Airport (RDU) had scored its 11th consecutive day of measurable rain, a mark reached seven other times since records began in the area in 1887. If it rains on Monday as predicted, RDU will tied its record-longest wet streak of 12 consecutive days, recorded from July 28 to August 8, 1887.

What’s causing the Carolina rains?
There isn’t just one culprit behind the incredible rains befalling the Carolinas--it is a multifactoral event, with several weather features coming into play. A new post by WU contributor Lee Grenci analyzes why the event is neither #Joaquin nor #NotJoaquin. Another WU blogger, Marshall Shepherd, outlines the connections between this event and the notorious “atmospheric river”--a feature behind some of the world’s heaviest mid-latitude rain events--in this article at Forbes.com. See also the Weather Channel’s comprehensive coverage of this event at weather.com, which will be frequently updated today and Monday.

Hurricane Joaquin approaching Bermuda
Conditions are rapidly deteriorating on Bermuda as Hurricane Joaquin draws closer, as seen on Bermuda radar. Now down to Category 2 strength, with top sustained winds of 105 mph as of 2:00 pm EDT Sunday, Joaquin was located about 125 miles southwest of Bermuda. Joaquin will be passing just west of the island, putting Bermuda on the more dangerous right-hand side of the storm, and the island remains in a hurricane warning. However, it appears Joaquin may move just far enough west to spare Bermuda from sustained hurricane-level conditions, as hurricane-force winds extend only about 60 miles from the center. Bermuda International Airport reported winds gusting to 55 mph around 3 pm ADT (2 pm EDT), with sustained winds near tropical storm strength (39 mph). After passing Bermuda, Joaquin should continue zipping across the Atlantic as it evolves into an extratropical storm.


Figure 4. Visible satellite image of Hurricane Joaquin at 1845Z Sunday, October 4, 2015. Bermuda is the small magenta area just northeast of Joaquin’s core. Image credit: NOAA/NESDIS.


Figure 5. Lt. Col. Keith Gibson, a pilot with the Air Force 53rd Weather Reconnaissance Squadron, pilots his C-130 hurricane hunter aircraft into Hurricane Joaquin on Saturday, October 3, 2015. On Friday, an Air Force hurricane hunter plane spiraled down from its penetration altitude of 10,000 in the eye to a altitude of 800 - 1000 feet, in order to search for the missing ship, El Faro. The ship, with a crew of 33, is still missing. Image credit: Air Force Reserve Hurricane Hunters.

Tropical Storm Oho likely to angle southeast of Hawaii
Despite unusually warm sea-surface temperatures, Tropical Storm Oho was apparently hindered from strengthening on Saturday by interaction with a large and strong band of convection extending well to its southeast. Bigger than Oho itself, this band was embedded within strong southwesterly monsoon flow, creating a setup more typical to the Northwest Pacific than the normally cooler and more stable Central Pacific. Strong wind shear also took its toll on Oho. The intense rainband has since weakened and moved further away, and Oho--now looking much more like a typical tropical storm, with a well-defined central core of convection--is projected to approach hurricane strength over the next several days as it moves mainly to the northeast. While models diverge somewhat on the particulars of Oho’s track, all dynamical and statistical models keep the storm well southeast of Hawaii. Oho’s remnant circulation could inject energy and moisture into a large, intense Pacific trough that will be approaching the Pacific Northwest more than a week from now.


Figure 6. Infrared image of Tropical Storm Oho from 1900 GMT Sunday, October 4. Image credit: NOAA/NESDIS.

In the Central Atlantic: Invest 91L
It’s late in the season for Cape Verde-type systems moving across the tropical Atlantic, but Invest 91L is trying to buck the odds. At present, 91L is little more than a large area of disorganized convection. Track models take 91L on a gradual curve north of the Lesser Antilles over the next five days. NHC gives 91L a 10% chance of development through Tuesday and a 30% chance through Friday. None of the leading long-range dynamical models develop 91L substantially during the upcoming week; this, plus climatology, suggests that 91L is unlikely to amount to much, although some models do intensify 91L toward the 4- to 5-day period.

A forecaster’s worst nightmare: Typhoon Mujigae intensifies to Cat 4 just before landfall
On Saturday, Typhoon Mujigae was forecast to hit Zhanjiang, China, about 200 miles west of Hong Kong, as a Category 1 storm. However, in the twelve hours before landfall, Mujigae surprised forecasters by rapidly intensifying from a Category 1 storm with 90 mph winds to an extremely dangerous Category 4 storm with 130 mph winds, and made landfall on the north side of the city of Zhanjiang near 1 am EDT Sunday (05 UTC.) An unexpected rapid intensification just before landfall in a heavily populated area is every hurricane forecaster's nightmare, and with Zhanjiang'a population being 7 million, there is the potential that Mujigae caused heavy loss of life and severe damage due to lack of preparedness for a Category 4 typhoon. The airport in Zhanjiang, which appears to have just missed getting hit by the weaker southern eyewall of the typhoon, recorded sustained winds of 65 mph at 2 pm Sunday local time, and rainfall of 5.20". The embedded tweet below shows Mujigae making landfall.

We’ll be back with our next update on Monday.

Bob Henson and Jeff Masters




Hurricane Flood

Landslide in Guatemala Kills 86, Leaves 500+ Missing

By: Jeff Masters , 1:25 PM GMT on October 04, 2015

One of the deadliest weather disasters of 2015 occurred in a suburb of Guatemala City, Guatemala on Thursday night, October 1, when a massive landslide of waterlogged earth and debris tore through the village of El Cambray II, in the municipality of Santa Catarina Pinula, destroying or damaging 125 homes. At least 86 were killed, and over 500 people were feared missing as of Sunday morning. According to Norman Avila of climaya.com, who maintains a personal weather station a few miles from the disaster site, the rains over the past three weeks in the region were not exceptional--6.72" during the period September 12 - October 1, and only 0.02" the day of the disaster. This is not an unusual amount of rain for a 3-week period during the May - October rainy season. In fact, conditions during this year's rainy season have been on the dry side, due to the influence of the strong El Niño event underway in the Eastern Pacific. The disaster seems to be primarily attributable to the location of the town, which is at the bottom of a canyon. According to a news report from Yahoo News, municipal authorities had urged the community, about 15 kilometers (10 miles) east of the capital Guatemala City, to relocate several times, most recently in November of 2014. According to EM-DAT, only three weather-related disasters have killed more than 400 people in Guatemala: floods in October 1949 that killed 40,000, Hurricane Stan of 2005 (1513 killed), and flooding from Pacific Hurricane Paul of 1982 (620 killed.) According to Aon Benfield, only two weather-related disasters have killed more than 200 people this year: a May heat wave in India (2,500 deaths), and a June heat wave in Pakistan (1,265 deaths.)


Figure 1. The deadly landslide of October 1, 2015, in a suburb of Guatemala City, Guatemala. Image credit: Soy 502 on Twitter.

Bob Henson will have a post by mid-afternoon on the tropics and on the extreme flood situation in South Carolina, which has experienced 1-in-1000 year rainfall amounts of over two feet of rain over the past two days.

Jeff Masters

Flood

Joaquin Close to Category 5 Strength; Rains Inundate Carolinas

By: Bob Henson , 6:01 PM GMT on October 03, 2015

There is plenty of life left in Hurricane Joaquin as it moves away from the Bahamas. An Air Force Hurricane Hunter aircraft detected winds around noon EDT Saturday of 144 knots at the 700-millibar level, with stepped-frequency microwave radiometer (SFMR) data showing estimated surface winds of 138 knots (159 mph). The National Hurricane Center upgraded Joaquin’s strength to top sustained winds of 155 mph in a special advisory at noon EDT Saturday, up from 130 mph in the advisory issued just an hour earlier. This immediately pushed Joaquin from the bottom to the top end of the Category 4 scale. A central pressure of 933 millibars was reported, although a radiosonde deployed in the eye of Joaquin failed, so there is some uncertainty around this estimate. Another Hurricane Hunter aircraft was en route to Joaquin as of early Saturday afternoon. Joaquin’s eye has warmed and cleared over the last few hours, reflecting the rapid restrengthening, although infrared satellite imagery shows that its core of strongest thunderstorms has become smaller and less intense.


Figure 1. MODIS image of Hurricane Joaquin heading away from the Bahamas as seen from NASA's Terra satellite on Saturday, October 3, 2015, at approximately 1:30 pm EDT. At the time, Joaquin had top winds of 155 mph. Image credit: NASA.

Joaquin’s burst of strength is especially remarkable given that a strong El Niño is under way (El Niño tends to suppress Atlantic hurricane activity by enhancing wind shear). The last Atlantic storm with sustained winds this strong was Hurricane Igor, in 2010, which peaked at 155 mph. The Atlantic’s last Category 5 was Hurricane Felix, in 2007, with winds topping out at 160 mph. The last El Niño season that managed to produce a Category 5 was 2004, when Ivan formed. However, the El Niño event of 2004-05 was relatively weak, with autumn Niño3.4 anomalies of only around +0.7°C compared to the current value of more than +2.0°C.

Joaquin is also in an area where very few Category 5 track segments have been reported since reliable records began in 1950 (see Figure 2). Record-warm waters in this part of the Northwest Atlantic are likely playing a major role in Joaquin’s unusual strength. Joaquin was designated as a tropical depression on Sunday night, September 27, at latitude 27.5°N. This makes Joaquin one of the strongest Atlantic hurricanes on record to have begun its life as a tropical cyclone at such a high latitude. In fact, Joaquin’s latest location (26.4°N. 70.9°W) is still south of its origin point.

Fortunately for the United States, Joaquin is hustling into the open Atlantic, now moving northeast at 16 mph. Track models are fairly consistent in keeping Joaquin west of Bermuda, but with only a small margin for error. Bermuda is now under a hurricane watch and tropical storm warning; at a minimum, the island can expect high surf, strong winds, and a few squalls from outer-edge rainbands, especially as Joaquin makes its closest approach on Monday.


Figure 2. In this map of all Category 5 hurricanes reported in the Atlantic since 1950, bright purple indicates the segments where Category 5 strength was analyzed. Image credit: The Weather Channel, courtesy Jon Erdman.


Figure 3. Satellite image Hurricane Joaquin taken at noon EDT October 3, 2015. At the time, the hurricane was just below Category 5 strength with top winds of 155 mph. A band of very heavy rain can also been seen feeding into South Carolina, to the northwest of the hurricane. Image credit: NASA/GSFC.


Figure 4. Flooding from heavy rain swamps the intersection of Huger Street and King Street in Charleston, S.C. on Saturday, October 3, 2015. Image credit: Matthew Fortner/The Post And Courier, via AP.

Severe flooding likely in South Carolina Saturday and Sunday
As expected, a band of torrential rain has materialized over South Carolina, paving the way for an especially dangerous situation from Saturday afternoon into Sunday. As of midday Saturday, the heaviest rain extended from the south half of the South Carolina coastline northwest across the state to the hilly Uplands region. The swath of intense rain will pivot very slowly in a counterclockwise direction, gradually translating southward over the higher terrain but moving very little near the coastline. This will put the area around Charleston at particular risk of severe flash flooding from Saturday afternoon into Sunday. CoCoRaHS maps show widespread rain totals of 4” - 8” in the Charleston area from 7:00 am EDT Friday to 7:00 am Saturday.


Figure 5. Predicted 15-hour rainfall totals from the HRRR model for the period from 10:00 am Saturday, October 3, to 1:00 am Sunday, October 4. Image credit: NWS/NCEP.


The Charleston area has a reasonable chance of beating the all-time three-day rainfall records below, possibly in just a 24-hour period!

North Charleston, SC (CHS)
11.95”, 6/9/1973-6/11/1973
11.62”, 6/10/1973-6/12/1973
11.40”, 9/19/1998-9/21/1998
10.64”, 9/4/1987-9/6/1987
10.52”, 9/21/1998-9/23/1998
Records begin in 1938

Downtown Charleston, SC (CXM)
12.39”, 6/9/1973-6/11/1973
11.92”, 6/10/1973-6/12/1973
11.73”, 9/5/1933-9/7/1933
11.72”, 9/4/1933-9/6/1933
11.31”, 9/4/1987-9/6/1987
Records begin in 1870

According to the Charleston NWS office, the record 24-hour rainfall for the state of South Carolina is 14.80", observed at Myrtle Beach during Hurricane Floyd on September 16, 1999.

Forecasters are particularly concerned that high-tide cycles in Charleston may coincide with periods of torrential rain, which could produce extreme flash flooding in the city in short order. The Saturday afternoon high tide of 8.2 feet was the highest to occur since Hurricane Hugo in 1989. The next tides will occur in Charleston at 1:34 am and 2:03 pm on Sunday.

Surrounding states are also experiencing heavy rain and flood threats. Mudslides and landslides are possible in the higher terrain of Georgia, South Carolina, and North Carolina. A strengthening of the onshore flow that has persisted for several days over the mid-Atlantic will again raise the risk of significant tidal flooding from Virginia to New Jersey, especially in the Hampton Roads area of Virginia.


Figure 6. GOES-West infrared satellite image covering the Northeast and Central Pacific, taken at 1545Z (11:45 am EDT) Saturday, October 3, 2015. Image credit: CIMMS/SSEC/University of Wisconsin-Madison.

Tropical Storm Oho may threaten Hawaii
The hyperactive Central Pacific broke its record--again--for the most number of named storms in a single season with the christening of Tropical Storm Oho on Saturday. According to NHC’s Eric Blake, Oho is the eighth tropical storm to form in the Central Pacific this year, doubling the previous record of just four. Oho is now located roughly 500 miles south-southeast of Honolulu. The steering patterns that will drive Oho are ill-defined and still evolving, which complicates the track forecast. The Central Pacific Hurricane Center currently projects Oho to arc northwest over the next couple of days, then move more briskly toward the east and northeast on a path that would keep it a couple hundred miles south of Hawaii’s Big Island early next week. There is plenty of room for this forecast to evolve, though. Oho has the chance to become a powerful hurricane, thanks to the weak upper-level flow as well as record-warm waters that have fueled so many other tropical cyclones in the Central Pacific this year. The SHIPS rapid intensification index gives Oho a good chance of rapidly strengthening from Saturday into Sunday. Oho now has top sustained winds of just 40 mph, but most dynamical and statistical models are making Oho a hurricane by Monday, and several bring it to Category 2 status by Thursday.

Elsewhere in the tropics
An array of other systems peppered the Northern Hemisphere tropics on Saturday. In the Central Atlantic, Invest 90L is looking less robust, with NHC now giving it only a 40% chance of development in the next 2 to 5 days. A late-blooming Cape Verde wave between 30°W and 35°W poses little threat over at least the next several days, and strong wind shear at low latitudes will probably cap any later development.


Figure 7. WU’s latest tracking map for tropical cyclones around the globe.

In the Northeast Pacific, Invest 94E is slowly organizing more than 1000 miles southwest of Baja California. NHC gives 94E a 30% chance of developing into a tropical cyclone by Monday and a 50% chance by Thursday. Closer to Mexico, the remants of Tropical Storm Marty could produce heavy rainfall as they move inland on Sunday into Monday. Some moisture from ex-Marty may get entrained into an upper-level storm taking shape early next week in the Southwest U.S., possibly delivering strong thunderstorms to the Arizona deserts on Monday.

In the Central Pacific, still another system--Tropical Depression 8C, the 13th tropical cyclone to develop in or pass through the Central Pacific this year--formed on Saturday morning about 1100 miles southwest of Honolulu. Moderate southerly shear should keep 8C from developing beyond minimal tropical-storm strength for at least the next couple of days as it pushes westward.

In the Northwest Pacific, Typhoon Mujigae may strengthen slightly over the next 24 hours before it moves into the coast of extreme southern China, southwest of Hong Kong. To the east, Tropical Storm Choi-Wan will slowly gather steam and may become a minimal typhoon early next week before an expected recurvature just east of Japan by midweek.

We’ll have our next update on Sunday afternoon.

Bob Henson

Hurricane Flood

Joaquin Still Gripping Bahamas; #NotJoaquin Dousing Carolinas, Virginia

By: Bob Henson and Jeff Masters , 11:16 PM GMT on October 02, 2015

A potentially historic rainfall event for the Carolinas has begun, with many locations set to receive between 1 and 2 feet of rain by early next week. An intense band of thunderstorms has set up across eastern NC and northeast SC, and cells are “training” northward through this N-S band, already leading to high rainfall totals. A station at North Myrtle Beach, SC, reported 8.03” in the 24 hours up through 6:24 pm EDT Friday. More than half of that amount (4.30”) fell during the last two hours of that period.


Figure 1. Composite NWS/NEXRAD radar image from 2215Z (6:15 pm EDT) Friday, October 2, 2015. Image credit: WU’s Storm app for iPad.

The culprits behind this unique event are an upper-level low cutting off across the Florida Panhandle; a preexisting frontal boundary along the U.S. East Coast; and a flow of deep, rich tropical moisture, including some from Hurricane Joaquin (see below), streaming into the region. As the upper low slowly moves across the region, a weak surface low will form along the boundary somewhere near the South Carolina coast, causing the most intense swath of rainfall to pivot around its north side across the Carolinas.

When the frontal zone hits the mountainous western part of the state, upslope flow will add to the rainfall intensity and exacerbate the potential for landslides and mudslides. Models suggest that the strength of the inflow of moist air into this system is at record or near-record values for the time of year; wind speeds at the 850-millibar level (about a mile above the surface) are projected to be as high as 75 mph by Sunday. The projected rainfall amounts are in line with these extreme values (see our morning post for more details).

Does the Carolinas storm qualify as a “nor’easter”? Strictly speaking, it does: the AMS glossary defines “nor’easter” (“northeast storm”) simply as “a cyclonic storm of the east coast of North America, so called because the winds over the coastal area are from the northeast.” The term is most often used in connection with winter storms at more northerly U.S. locations. Another term for the event, quickly taking hold on Twitter, is #NotJoaquin.


Figure 2. The Congaree River at Carolina Eastman, about 10 miles south of downtown Columbia, SC, is projected to approach its record crest of 126.9 feet by late Monday. Image credit: NWS Advanced Hydrologic Prediction Service.

Major coastal/tidal flooding under way in Hampton Roads
The lower Chesapeake Bay region of Virginia is seeing one of its worst flood events in years, as persistent onshore flow is pushing water into the region through multiple tidal cycles. Heavy rainfall in the vicinity is only making matters worse. Coastal and tidal flooding will persist during the weekend from New Jersey to North Carolina, with conditions expected to be the worst in coastal Virginia, including the Hampton Roads area surrounding Norfolk. Extensive street flooding has already been observed in many low-lying parts of the region, and the situation may deteriorate further over the weekend, especially as surface low pressure wraps up in the Carolinas and the onshore flow intensifies on Sunday. See our morning post for more on the particulars behind this unfolding situation.


Figure 3. Quinn Hurt looks across Atlantic Avenue as he attempts to cross the flooded street in Wachapreague, VA, on Friday, October 2, 2015. Wachapreague is located on the Atlantic shore toward the south end of the Delmarva peninsula. Image credit: Jay Diem/The Daily Times, via AP.


Figure 4. MODIS image of Hurricane Joaquin over the Bahamas as seen from NASA's Aqua satellite on Friday, October 2, 2015, at approximately 12:30 pm EDT. At the time, Joaquin had top winds of 130 mph. Image credit: NASA.


Figure 5. Hurricane Joaquin in the early morning hours of October 2, 2015, as photographed from the International Space Station. The lights of Miami are visible at the top. Image credit: Commander Scott Kelly, ISS.

Joaquin continues to rake Bahamas
Hurricane Joaquin was still hammering parts of the Central Bahamas late Friday. Joaquin is one of the strongest hurricanes known to affect the Bahamas during October, with Category 4 conditions affecting several islands for the better part of 24 hours. Joaquin was a Category 3 hurricane, with top sustained winds of 125 mph, as of the 5:00 pm EDT advisory from the National Hurricane Center. Joaquin was moving north at 10 mph, but infrared satellite imagery shows that Joaquin’s showers and thunderstorms have expanded and intensified over the last several hours, so heavy rain and high winds are no doubt continuing to strafe much of the Central Bahama Islands. Joaquin’s center passed almost directly over the island of San Salvador late Friday afternoon, as a weather station there reported a pressure of 944.3 mb (27.88”). The eyewall of Joaquin affected Crooked Island/Acklins Island (population 600), and Long Island (population 3,000) for many hours, and no doubt damage is heavy to extreme on those islands. A cargo ship named El Faro, with 33 crew members aboard, has gone missing en route from Jacksonville, FL, to Puerto Rico. The last report from the ship, on Thursday, indicated that it had lost power and begun to list while located near Crooked Island, which would put it in or near the slow-moving eyewall of Joaquin. Two Air Force Hurricane Hunter aircraft were unsuccessful in attempts to locate the ship on Friday afternoon.

Wunderground member ExumaMET, located on the island of Exuma, posted this update on Friday afternoon:

“Joaquin had been giving us one good final lashing that coincided with the flood tide. Some spots on Exuma are seeing 5-6 foot surges and an entire portion of George town is under water. The back of my house is protected by an extensive mangrove system and I actually have 5 foot swells running. Also there have been at least 2 cruising yachts that have sunk in George town with more that have broken their moorings and are either drifting or already on the rocks. Makes me thankful this storm did not come west an extra 20 miles. I can't get through to anyone in Williams town to find out what the damage is like... They are the closest to where [Joaquin] passed. Going on my 3rd day without power.”


Figure 6. Satellite image of atmospheric water vapor, collected at 1915Z (3:15 pm EDT) Friday, October 2, 2015. A narrow channel of strong upper-level southerlies is positioned near the U.S. East Coast, ahead of a distinct upper-level low cutting off near the Florida Panhandle (the low’s swirl is visible in the tan color, denoting relatively dry air). An outflow channel can be seen running from Joaquin to the mid-Atlantic coast. Well to Joaquin’s east is an upper-level low, and even further out is Invest 90L, incorporating remnants of former Tropical Storm Ida. Image credit: NOAA/NESDIS.

Out to sea (knock on wood!)
With the 12Z Friday guidance, we can pretty much put to rest the idea that Joaquin will directly strike the Carolinas, an outcome that most models were projecting as recently as two days ago. All of the major dynamical and statistical track models used by the National Hurricane Center were moving Joaquin toward the north and northeast from its current location. In addition, nearly all of the GFS ensemble members (GEFS) show the offshore track. Even the possibility of a glancing blow to Cape Cod now appears to be a far-fetched solution, although Joaquin could move close enough to intensify the high surf and strong wind that will already cover a vast area to the hurricane’s north.

If you only had Figure 6, and no other pieces of evidence, you might be hard-pressed to imagine that Joaquin will be going out to sea. The NW-SE orientation of Joaquin’s outflow suggests that the hurricane is being tugged in the direction of the U.S. East Coast by the very strong south-southwest flow present there. However, the weak upper-level low evident to the northeast of Joaquin is the key. As it moves north in tandem with Invest 90L, located further east, this low will help create a pathway for Joaquin to zip north-northeast, parallel to the U.S. East Coast but far offshore. Joaquin may lose some of its classic symmetry on satellite as it gains speed, although it will remain a potent wind-producer for several days to come. The hurricane will also send powerful swells toward the U.S. East Coast throughout the weekend and into early next week.

We’ll be back with our next update on Saturday afternoon.

Bob Henson and Jeff Masters

Hurricane Flood

Thousand-Year Rains Possible in Carolinas; Joaquin Headed North

By: Jeff Masters and Bob Henson , 4:39 PM GMT on October 02, 2015

Hurricane Joaquin continued to lash the Bahamas on Friday morning as it turned north on a course expected to keep it well away from the U.S. East Coast. However, several days of coastal flooding and beach erosion will occur from New Jersey to North Carolina, and extremely heavy rain could produce dangerous impacts in South Carolina. It was a long night of screaming winds, pounding waves, and lashing rains for residents of the Central Bahama Islands, where dangerous Hurricane Joaquin maintained Category 4 intensity with 130 mph winds. The eyewall of Joaquin affected Crooked Island/Acklins Island (population 600), and Long Island (population 3,000) for many hours, and no doubt damage is heavy to extreme on those islands. Joaquin has turned to the north, as seen on microwave satellite animations, and as the storm plows northwards at 3 - 6 mph on Friday, San Salvador Island (population 900) will likely feel eyewall winds. The Hurricane Hunters made multiple passes through the hurricane Friday morning, finding that the central pressure had gradually risen from 935 mb to 939 mb. The size of the eye has been fluctuating considerably, and the Hurricane Hunters noted a secondary maxima of winds away from the eyewall, indicating that an eyewall replacement cycle may be ready to begin. These cycles that lead to a collapse of the inner eyewall, followed by a temporary weakening as a new outer eyewall is established. Wind shear continued to be in the moderate range, 10 - 20 knots, on Friday morning, and visible and infrared satellite loops showed that Joaquin continued to maintain a formidable appearance. Upper level winds analyses from the University of Wisconsin show that the hurricane has now has two impressive upper-level outflow channels, one to the northwest, and one to the southeast. Ocean temperatures in the region remain a record-warm 30°C (86°F). These conditions should allow Joaquin to maintain at least Category 3 strength until Saturday.


Figure 1. Lightning flashes in one of Hurricane Joaquin's spiral bands in this nighttime image taken in the early morning hours of October 2, 2015 from the International Space Station. The lights of Miami are visible in the upper left. Image credit: Commander Scott Kelly, ISS.


Figure 2.  GOES-13 visible image of Hurricane Joaquin taken at 8:45 am EDT October 2, 2015. At the time, Joaquin was a Category 4 storm with 130 mph winds. Image credit: NOAA Visualization Lab.

Forecast for Joaquin
Joaquin is finally embarking on its long-awaited turn toward the north, and the Bahamas are likely the only land areas that will feel a direct impact from the storm. Microwave satellite animations on Friday morning showed the convective core of Joaquin shifting toward the north of the center, and upper-level outflow is now streaming toward the northwest, some of it becoming entrained in the frontal system off the East Coast.

The 00Z Friday (8 pm EDT Thursday) computer model runs continued to lean heavily toward an offshore track for Joaquin. The 00Z GFS and ECMWF solutions inched slightly westward from their previous tracks, bringing Joaquin a bit closer to Cape Cod through a subtle left swing in its path. The 06Z GFS run shifted back toward the east, well away from New England, and the 12Z GFS run also remained far offshore. A slight northward bend in the otherwise northeastward track remains in the GFS, ECMWF, and UKMET solutions, as noted in the 11:00 am EDT forecast discussion from NHC. The ECMWF’s 00Z Friday ensemble runs were quite closely clustered around the offshore track, with only a couple of its 50 members suggesting the potential for a New England landfall. In contrast, more than a third of the 00Z and 06Z GEFS ensemble members continue to indicate the possibility of a SC/NC landfall, although the operational GFS model has not shown such a solution for some time. Among other major models, the Canadian GEM and the U.S. NAM (including the 12Z Friday NAM ran) also point toward an East Coast landfall, but take heed: these are historically among the least-reliable track models, so we would be wise to heavily discount them in favor of the GFS and ECMWF. 


Figure 3. GFS ensemble members from the GEFS run on 06Z Friday, October 2, lean heavily toward an offshore track for Joaquin as depicted in the official NHC forecast, although a few members still bring Joaquin along a looping onshore path near the U.S. East Coast. On the right-hand side are the ensembles’ projected tracks for Invest 90L. Image credit: NOAA Earth System Research Laboratory.

The official NHC forecast track as of 11:00 am EDT Friday keeps Joaquin hundreds of miles away from the U.S. East Coast, and NHC has enough confidence in this track that the “key points” section of its latest forecast discussion does not mention any potential for a U.S. landfall. The persistence of a few model outliers should not be a particular cause for concern at this point, but it does remind us that the upper-level features that will steer Joaquin are complex and dynamic. The two main influences on Joaquin’s track remain the upper low now cutting off over the Southeast U.S. and Invest 90L, located more than 1000 miles east of Joaquin. 90L originated from an upper-level low that has incorporated remnants of former Tropical Storm Ida. The NHC is giving 90L an 80% chance of developing into a subtropical or tropical cyclone over the next 48 hours as it drifts northward. The presence of 90L is creating a pathway for Joaquin to head northeast.

It appears that the strong jet stream diving around the Southeast low will kick eastward around the base of the low over the next couple of days, pushing the eastern part of the low offshore. Together with the influence of slowly developing 90L, this should keep Joaquin moving on a north to northeast track Friday and Saturday. As Figure 3 suggests, a more northeastward motion would lend confidence in the current expectation of an offshore track, while any significant component of motion toward the west today and Saturday would keep open the door for the far-less-likely possibility of a track hooking around the Southeast upper low. We’ll be watching the 12Z Friday model guidance closely and will have more on the forecast for Joaquin in our afternoon update.


Figure 4. Projected rainfall (in inches) for the 72-hour period from 12Z (8 am EDT) Friday, October 2, 2015, to Monday, October 5. Image credit: NOAA/NWS Weather Prediction Center.

Epic rainfall likely for South Carolina
The latest 3-day Quantitative Precipitation Forecast from NOAA's Weather Prediction Center is calling for 10 - 15" inches of rain for the majority of South Carolina, including the cities of Charleston and Columbia.
 
This forecast assumes that Hurricane Joaquin will not come anywhere close to the state. The rain will be due to what meteorologists call a "Predecessor Rain Event" (PRE) (see this paper on them, h/t to Stu Ostro of TWC: http://journals.ametsoc.org/doi/pdf/10.1175/2010MWR3243.1). In a Predecessor Rain Event, tropical moisture well out ahead of a landfalling tropical cyclone interacts with a surface front and upper-level trough to produce heavy rainfall, often with significant inland flooding. The PRE can develop well to the left or right of the eventual track of the tropical cyclone. Slow-moving Hurricane Joaquin is perfectly positioned to transport a strong low-level flow of super-moist tropical air that has water vapor evaporated from record-warm ocean waters north of the Bahamas westwards into the Southeast U.S. Once this moisture hits land, it will encounter a cut-off upper low pressure system aloft, with a surface front beneath it, which will lift the moist air, cooling it, and forcing epic amounts of rainfall to fall. The air will also be moving up in elevation from the coast to the Piedmont and Appalachians, which lifts the air and facilitates even more precipitation. Satellite imagery is already hinting at development of this connection of moisture between Joaquin and the Southeast low and frontal system.


Figure 5. The maximum rainfall predicted to fall in any 24-hour period during the 5-day period from 5 am EDT October 2 to 5 am EDT October 7, according to a high-resolution Weather Research Forecast (WRF) model run done by MetStat, Inc. (http://www.metstat.com.) In some areas of North Carolina and South Carolina, 24-hour rainfall amounts one would expect to fall only once in a thousand years are predicted. MetStat computed the recurrence interval statistics based on gauge-adjusted radar precipitation and frequency estimates from NOAA Atlas 14 Volume 8, published in 2013 (http://dipper.nws.noaa.gov/hdsc/pfds/.) MetStat does not supply their precipitation recurrence interval forecasts or premium analysis products for free, but anyone can monitor the real-time analysis (observed) at: http://metstat.com/solutions/extreme-precipitation-index-analysis/ or on their Facebook page.

Using about a century of precipitation records, NOAA has constructed a Precipitation Frequency Data Server, which estimates how often we might expect to see extreme rainfall events recur.  According to NOAA's Precipitation Frequency Data Server, these could be 1-in-1000 year rains for some locations. (Hydrologists would refer to a 1-in-1000-year rain as having a typical "recurrence interval" of 1000 years. The idea is that such events are not always separated by 1000 years; the same amount of rain could conceivably occur the very next year, or might not occur until thousands of years later.) The three-day 1-in-1000 year rainfall amounts for Charleston, Greenville and Columbia are 17.1", 17.8", and 14.2", respectively. The 24-hour 1-in-1000 year rainfall amounts for Charleston, Greenville and Columbia are 14.8", 15.9", and 12.5", respectively.

The storm to beat in South Carolina is Tropical Storm Jerry of 1995, which dumped up to 18.51" of rain over a small region of Southwest SC. The storm to beat in nearby eastern North Carolina is Hurricane Floyd, which dumped prodigious amounts of rain in mid-September 1999, less than a month after Hurricane Dennis had drenched the region. Floyd produced a broad stripe of 15" - 20" rains, with a maximum total of 24.06" at a site five miles north of Southport, NC (about 30 miles east of the NC/SC border). To get such widespread multi-day totals outside of a tropical cyclone would be a monumental feat.  Averaged across the state as a whole, the wettest three calendar months in South Carolina weather history are July 1916 (14.41"), September 1924 (13.16"), and September 1928 (12.70"). All of these were related to tropical cyclones passing through or near the state. If the NWS precipitation forecasts are in the right ballpark, then the first few days of October 2015 might approach or even exceed these all-time monthly records for the entire state--without any help from a landfalling hurricane or tropical storm!

Texas and Oklahoma have already notched their wettest months on record (by far) this past May, and Illinois had its second-wettest month on record in June. Our warming climate is making intense short-term rains (such as the highest 1-day totals) even heavier in many parts of the United States and the world, although less research has been done on trends in monthly rainfall.

For more on the science of extremely heavy rainfall, see Bob Henson's May 2015 post, The Rains of May and the Science of Recurrence Intervals.


Figure 6. Projected maximum flood category for the 24-hour period from noon EDT Friday, October 2, through Saturday, October 3, 2015. The worst impacts today through Saturday are expected through the southern part of the Chesapeake Bay. Image credit: NOAA/NWS Advanced Hydrologic Prediction Service.


Figure 7. Strong on-shore winds along the mid-Atlantic coast due to the pressure gradient between Hurricane Joaquin and a strong high pressure system over the Northeast U.S. were creating storm surge heights of 2 - 3' in many locations, and over 3' on Virginia's Delmarva Peninsula. Image credit: Hal Needham.

Long-duration coastal flooding under way
The combination of Hurricane Joaquin, the Southeast U.S. low, and a strong ridge well to the north is leading to an unusually prolonged period of steady onshore flow and high surf along the U.S. East Coast from New Jersey southward to North Carolina. The highest-impact coastal flooding and beach erosion can be expected along the Virginia and Delaware coast, including Ocean City, MD, and the Hampton Roads area of VA, which includes Norfolk and Virginia Beach. The Wakefield, VA, NWS office is calling for several rounds of moderate to severe coastal flooding through the weekend. See the latest blog post from storm-surge expert Hal Needham for more details on this event.

We’ll have an update later this afternoon.

Jeff Masters and Bob Henson

Hurricane Flood

Category 4 Joaquin Pounds the Bahamas; a U.S. Landfall Unlikely

By: Jeff Masters and Bob Henson , 9:22 PM GMT on October 01, 2015

Dangerous Hurricane Joaquin has intensified to a Category 4 storm with 130 mph winds and a 936 mb pressure, making it the strongest Atlantic hurricane in five years. The last stronger storm was Hurricane Igor of 2010, which bottomed out at 924 mb on September 15, 2010. Joaquin is now the second major hurricane of 2015 in the Atlantic, joining Hurricane Danny, which peaked as a Category 3 storm with 115 mph winds on August 21. Joaquin's motion has slowed to a 5 mph westward crawl over the Central Bahamas, which are receiving an epic pounding from the mighty hurricane. David Adams of Reuters told me this afternoon that he has been calling down to the Bahamas, and no phones are being answered on Aklins Island--but Reuters' Nassau correspondent informed him that flooding was bad on Aklins Island and Long Island. The last hurricane hunter aircraft departed the storm after a 12:47 pm EDT eye fix, and new plane will be in the storm early this evening. The Hurricane Hunters found that Joaquin's eye had shrunk from 41 miles in diameter early this morning to 27 miles in diameter this afternoon. Shrinkage of the eye is common in intensifying major hurricanes, and eyewall replacement cycles that lead to temporary weakening of the storms typically occur when the eye diameter gets down to about 10 miles. Wind shear continued to be in the moderate range, 10 - 20 knots, on Thursday afternoon, and visible and infrared satellite loops showed that Joaquin was a moderate-sized hurricane with impressive organization, with a solid core of intense eyewall thunderstorms surrounding a clear eye. Upper level wind analyses from the University of Wisconsin show that the hurricane has maintained an impressive upper-level outflow channel to the southeast, and it appeared a new outflow channel was ready to open up to the northwest, which would support continued intensification. Ocean temperatures in the region remain a record-warm 30°C (86°F), but may start to cool due to Joaquin's slow motion. This cooling of the waters could well put the brakes on further intensification by Friday morning.


Figure 1. GOES-13 visible image of Hurricane Joaquin taken at 3pm EDT October 1, 2015. At the time, Joaquin was a Category 4 storm with 130 mph winds. Image credit: NOAA Visualization Lab.

Two major Atlantic hurricanes during a strong El Niño: a first
Strong El Niño conditions currently exist in the Eastern Pacific, where ocean temperatures have warmed to 2.3°C above average in the region 5°N-5°S, 120°W-180°W (called the Niño 3.4 region). Major Atlantic hurricanes are uncommon when ocean temperatures get this warm in the Eastern Pacific, and 2015 is the first strong El Niño year to experience two major Atlantic hurricanes since El Niño records began in 1950. The other four years that had strong El Niño conditions during the peak August-September-October portion of hurricane season have had only one major hurricane each. Those years were 1972, 1982, 1987, and 1997. Joaquin is now the second strongest Atlantic hurricane observed during strong El Niño conditions, behind only Hurricane Debby of 1982, which had 135 mph winds.

Joaquin is an uncommon beast: a major hurricane that did not develop from an African tropical wave. These waves serve as the origin of about 85% of all Atlantic major hurricanes. According to TWC's Stu Ostro, Joaquin's origin can be traced, in part all the way back to a upper-level trough that came off the coast of the Carolinas on September 15 (animation here). This trough became a cold upper low northeast of the Leeward Islands, then warmed and transformed into a warm-cored tropical cyclone. These sorts of systems are usually too far north to have warm enough water temperatures to make it to major hurricane status, but with the waters of Joaquin's birth a record warm 30°C (86°F), this was not a problem for the storm.

Impact of Joaquin on the Bahamas
Joaquin's main threat to the Bahamas is likely to be wind damage. The 5 pm Thursday Wind Probability Forecast from NHC gave the highest chances of hurricane-force winds of 69% to San Salvador Island (population 930). Hurricane-force winds are slightly less likely on Cat Island (population 1,500), to the northwest of San Salvador Island. Heavy rains of 10 - 15 inches in the Central Bahamas may also cause considerable flooding damage, as well as the large waves of the storm riding up on top of the expected 5 - 10' storm surge.


Figure 2. This Maximum Water Depth storm surge image for the Bahamas shows the worst-case inundation scenarios for a Category 4 hurricane with 145 mph winds, as predicted using dozens of runs of NOAA's SLOSH model. For example, if you are inland at an elevation of ten feet above mean sea level, and the combined storm surge and tide (the "storm tide") is fifteen feet at your location, the water depth image will show five feet of inundation. No single storm will be able to cause the level of flooding depicted in this image. The regions of the Bahamas most vulnerable to storm surge tend to lie on the southwest sides of the islands. Since Joaquin is approaching from the northeast, the storm's peak on-shore winds will be affecting the northeast sides of the islands, where deeper offshore waters tend not to allow larger storm surges to build. NHC is forecasting peak water levels (the depth of water above the high tide mark) of 5 - 10 feet from Joaquin in the Bahamas. See wunderground's storm surge pages for more storm surge info.

Joaquin likely to miss the U.S.
Confidence is growing that Joaquin will move out to sea this weekend, although a U.S. landfall still cannot be ruled out. Among the 12Z (8 am EDT) Thursday operational runs, three models--the Canadian GEM and the U.S. GFDL and NAVGEM models—continue to call for a landfall on the U.S. East Coast. Other models, including the four that performed the best for three-day outlooks during the 2014 Atlantic hurricane season (GFS, ECMWF, HWRF, and UKMET), now agree that Joaquin will turn sharply toward the north or northeast and begin to accelerate by late Friday or Saturday, feeling the influence of an upper-level low drifting well to the northeast. The less-likely possibility of a U.S. landfall hinges on the idea that a strong upper-level trough would produce a cut-off low in the Southeast that would hook Joaquin around it, much as happened with Hurricane/Superstorm Sandy in 2012. That cut-off low is still expected to form, but the balance between the eastern U.S. low and the Atlantic low in terms of influence on Joaquin now appears to favor the latter.
 
NHC nudged the forecast track for Joaquin further east in its 5:00 pm EDT outlook. In the associated discussion, they stressed: “We are becoming optimistic that the Carolinas and the mid-Atlantic states will avoid the direct effects from Joaquin.  However, we cannot yet completely rule out direct impacts along on the east coast, and residents there should continue to follow the progress of Joaquin over the next couple of days.”


Figure 3. The European model ensemble run at 8 pm EDT Wednesday September 30, 2015 (00Z Thursday, October 1) had four of its 50 members (grey lines) that tracked the movement of Joaquin exceptionally well during the period 00Z - 18Z October 1. All of these four members had tracks for Joaquin that missed the U.S., with one of them hitting Canada. The operational (high-resolution) version of the European model is shown in red. Image taken from a custom software package used by TWC.
 
Historic rain/flood/surge still in the cards for U.S. East Coast
Joaquin’s presence, even at sea, is one of many factors now lining up to help produce a weather event that may rival many U.S. Category 1 hurricane landfalls in terms of impact. Along the immediate coast from New Jersey to the Carolinas, several days of high seas, beach erosion, and coastal flooding can be expected from a long fetch of easterly wind setting up between Joaquin and a strong, sprawling ridge of high pressure far to its north. The concern is not so much the intensity of the onshore flow (assuming Joaquin does not approach) but its sheer persistence. “The duration of this wind event is absolutely mind-boggling,” said storm-surge expert Hal Needham in a blog post on Thursday morning. Onshore winds of more than 20 mph could be affecting the mid-Atlantic coast for more than 96 solid hours, regardless of Joaquin’s track. High water will be present for as many as 10 high tides over several days, increasing the risk of erosion and flooding along the coast as well as up to a few miles inland. “This developing situation is truly historic and has not been observed in the modern history of the Mid-Atlantic Coast,” says Needham.



Figure 4. The combination of Hurricane Joaquin and high pressure well to its north will put a squeeze play on the U.S. East Coast, with several days of onshore flow expected to produce high surf and coastal flooding. This map shows surface winds in knots (multiply by 1.15 for mph) predicted by the 12Z Thursday run of the GFS model for 06Z (2:00 am EDT) Sunday, October 4. Image generated by wundermap using “model data” option.
 
Another exceptional part of the story from this weekend into Monday will be the mammoth rainfall amounts expected to fall over parts of the Southeast and mid-Atlantic, particularly South Carolina. These areas are not unfamiliar with torrential rain, especially from landfalling tropical cyclones, but the amounts this weekend will be amazing even by southeastern standards—and this is assuming Joaquin does not make landfall. Strong and extremely moist flow pushing from the Atlantic against the Appalachians may boost rainfall totals to record or near-record totals from the mountains and foothills of northeast Georgia to western Virginia. The Greenville/Spartanburg NWS office is already warning that “all the ingredients are in place for a rainfall event of historic proportions across the area.”
 
At the same time, a frontal boundary may develop between relatively cool air associated with the Southeast upper low and warmer, more humid air being funneled across the Carolinas from Joaquin’s circulation. This boundary, which should extend east or southeast from the Appalachians to the Atlantic, will help the extremely heavy rain to extend into the coastal plains of the Carolinas. According to Peter Neilley (WSI), the boundary may end up bearing some resemblance to the “norlun trough” feature that can boost snow amounts in nor’easter winter storms.
 
With onshore flow pushing a storm surge of 1 - 2' along much of the East Coast over the next five days, the rain water will not be able to drain effectively into the ocean, causing rivers to back up and flood more severely than they otherwise would. A mandatory evacuation is now in effect for Ocrakoke Island in North Carolina’s Outer Banks, out of concern about rising water levels in the Pamlico Sound that separates the Outer Banks from the NC mainland. Transportation could be hindered for days in coastal regions by this complex setup, and there is the potential for major flash flooding and river flooding throughout much of the Carolinas depending on the timing and placement of the heaviest rains.
 

Figure 5. 5-day rainfall amounts for the period from 8:00 pm EDT Thursday, October 1, to Tuesday, October 6. Almost all of South Carolina is projected to get 10” – 20” of rain. This map assumes that Hurricane Joaquin will remain offshore from the U.S. East Coast. Image credit: NWS Weather Prediction Center.

Value of the Hurricane Hunters
The Hurricane Hunters have been in Joaquin almost continuously the past two days, sending back invaluable information on the storm's position and intensity. Without their data, we might well have classified Joaquin as a much weaker storm, since satellite estimates of Joaquin's strength were too low during a large portion of the hurricane's intensification period. Satellite estimates of Joaquin's strength using the Dvorak technique from NOAA/NESDIS gave the hurricane a constant rating of T5.0 between Wednesday evening at 7:45 pm EDT and Thursday morning at 7:45 am EDT. The Tropical Storm Current Intensity Chart for this corresponds to a Category 2 hurricane with 105 mph winds and a 970 mb pressure. During this period, the Hurricane Hunters documented that Joaquin actually underwent a period of rapid intensification, with a pressure drop from 954 mb to 942 mb, and winds increasing from 105 mph to 125 mph. However, by 2 pm EDT Thursday, the satellite estimates of Joaquin's strength finally matched what the Hurricane Hunters were seeing, with both saying top winds of 130 mph.

Bob Henson will be on WUTV on the Weather Channel at 6:20 pm EDT Wednesday, and Jeff Masters will be on at 8:20 pm.

Wunderblogger Steve Gregory has a detailed Thursday afternoon update on Joaquin.

Jeff Masters and Bob Henson

Hurricane

Joaquin Hammers Bahamas; Future Track Still Uncertain

By: Jeff Masters and Bob Henson , 4:06 PM GMT on October 01, 2015

Category 3 Hurricane Joaquin is giving the Central Bahama Islands a ferocious pounding as the storm moves very slowly over the islands. An Air Force hurricane hunter aircraft made three penetrations of Joaquin's center on Thursday morning, and found top surface winds of 125 mph. The central pressure held steady at 942 mb between the first two passes at 7:47 and 9:23 am EDT, but dropped to 939 mb at 11:20 am, so Joaquin is still intensifying. The hurricane had a large 36-mile diameter eye that was fully closed in their second pass through. Joaquin took advantage of wind shear that had fallen to the moderate range, 10 - 20 knots, on Thursday morning. Visible and infrared satellite loops show that Joaquin is a moderate-sized hurricane with impressive organization, with a solid core of intense eyewall thunderstorms surrounding a clear eye. Upper level winds analyses from the University of Wisconsin show that the hurricane has maintained an impressive upper-level outflow channel to the southeast, which allowed the hurricane's rapid intensification over the past 24 hours. Ocean temperatures in the region remain a record-warm 30°C (86°F), but may start to cool due to Joaquin's slow motion.


Figure 1. GOES-13 image of Hurricane Joaquin over the Bahamas as seen on Thursday, October 1, 2015, at 10:30 am EDT. At the time, Joaquin had top winds of 125 mph. Image credit: NASA/GSFC.


Figure 2. Winds were rising across the Central Bahamas on Thursday morning, and were a brisk 39 mph, gusting to 58 mph, at 3:13 am EDT at a personal weather station on Exuma Island. Shewp's Webcam from Exuma Island on Thursday morning showed a darkening sky with heavy whitecapping of the waters, as Joaquin approached, but the webcam and weather station stopped reporting at 8:52 am.

Impact of Joaquin on the Bahamas
Joaquin's main threat to the Bahamas is likely to be wind damage. The 11 am Thursday Wind Probability Forecast from NHC gave the highest chances of hurricane-force winds of 69% to San Salvador Island (population 930). Hurricane-force winds are slightly less likely on Cat Island (population 1,500), to the northwest of San Salvador Island. Heavy rains of 10 - 15 inches in the Central Bahamas may also cause considerable flooding damage, as well as the large waves of the storm riding up on top of the expected 5 - 10' storm surge. Thursday morning satellite imagery showed that Joaquin had stalled out over the Central Bahamas; with only a slow motion expected for the next day, the islands will receive and extended pounding, increasing the odds of significant wind damage.


Figure 3. This Maximum Water Depth storm surge image for the Bahamas shows the worst-case inundation scenarios for a Category 3 hurricane with 120 mph winds, as predicted using dozens of runs of NOAA's SLOSH model. For example, if you are inland at an elevation of ten feet above mean sea level, and the combined storm surge and tide (the "storm tide") is fifteen feet at your location, the water depth image will show five feet of inundation. No single storm will be able to cause the level of flooding depicted in this image. The regions of the Bahamas most vulnerable to storm surge tend to lie on the southwest sides of the islands. Since Joaquin is approaching from the northeast, the storm's peak on-shore winds will be affecting the northeast sides of the islands, where deeper offshore waters tend not to allow larger storm surges to build. NHC is forecasting peak water levels (the depth of water above the high tide mark) of 5 - 10 feet from Joaquin in the Bahamas. See wunderground's storm surge pages for more storm surge info.

Outlook for Joaquin: Out to sea?
With favorable conditions for at least the next day (low wind shear and very warm sea-surface temperatures), Joaquin may yet intensify further. The 11 am EDT Thursday advisory from NHC pegs Joaquin’s top sustained winds at 125 mph, and the NHC outlook brings Joaquin to Category 4 status, with top sustained winds of 140 mph projected by Friday. Joaquin is located close to the region where Hurricane Andrew grew from Category 1 to Category 5 status during a year with very suppressed hurricane activity, 1992 (featuring an El Niño event during the first half of the year.) This serves as a reminder that the subtropics can be a worrisome breeding ground for strong hurricanes even during an El Niño year, when activity in the deep tropics tends to be suppressed. We can expect some fluctuation in strength if an eyewall replacement cycle takes hold over the next day or two, as is common after hurricanes go through a rapid intensification phase. Once Joaquin begins moving northward under the influence of stronger upper-level flow, we can expect its top sustained winds to eventually decrease while the size of its wind field increases. The waters are unusually warm across much of the Northwest Atlantic, which may help Joaquin sustain its strength longer than one would otherwise expect.

The track forecast for Joaquin remains low-confidence, although there was an important shift in the 00Z and 06Z Thursday computer-model guidance in favor of keeping Joaquin away from the U.S. East Coast. The global-scale GFS model, which had been predicting a North Carolina landfall for more than a day, shifted in its 00Z Thursday run to a track toward Long Island. The 06Z Thursday run of the GFS showed an even more dramatic shift eastward, with Joaquin hugging the Nova Scotia coastline. Members of the GFS ensemble also reflected this shift, with most but not all of the 06Z GEFS members showing an offshore track. (Ensembles are produced by running a model many times, each with slightly different initial conditions to represent uncertainty in the atmosphere’s starting point.) The UKMET also shifted significantly eastward, moving from a North Carolina landfall in its 12Z Wednesday run to a Cape Cod brushing in its 00Z Thursday run. The high-resolution HWRF and GFDL models stuck to their guns, with their 06Z Thursday runs continuing to depict landfall in North Carolina or Virginia.

If the trend toward an offshore track holds up in Thursday’s model guidance, kudos must go to the ECMWF model. Its operational run has consistently called for a track well away from the U.S. East Coast, as was the case at 00Z Thursday. Just as significant, most of the ECMWF ensemble members (about 40 out of 50) showed an offshore track in the 00Z Thursday runs, whereas a large part of the ensemble had previously shown of a U.S. landfall. Analyses of the ECMWF ensemble for 12Z Wednesday and 00Z Thursday indicate that the ensemble members who did the best in the first few hours of the forecast were consistently taking Joaquin offshore (see Figure 6).


Figure 4. The latest runs from our two top models for forecasting hurricane tracks: the 8 pm EDT Wednesday September 30, 2015 (00Z Thursday) run of the European model (left), and the 2 am EDT October 1 (06Z) run of the GFS model (right) both took Joaquin on a path out to sea that misses the U.S. coast, but were still very far apart. Image credit: wundermap with the "Model Data" layer turned on.





Figure 5. The ensemble runs of our two top models for forecasting hurricane tracks, both run at 8 pm EDT Wednesday September 30, 2015 (00Z Thursday). The 50 members of the European model ensemble (top) had only about 10 of its 50 members that showed a U.S. landfall, while about 10 of the 20 members of the GFS model ensemble (bottom) did so. Compared to the runs done 24 hours previous, the European ensembles had shifted considerably to the east, away from the U.S., with the GFS ensemble members less so. Ensemble runs take the operational version of the model and run it at lower resolution with slightly different initial conditions, to generate an "ensemble" of possible forecasts. 




Figure 6. The European model ensemble run at 8 pm EDT Wednesday September 30, 2015 (00Z Thursday, October 1) had four of its 50 members (grey lines) that tracked the movement of Joaquin exceptionally well during the period 00Z - 12Z October 1. All of these four members had tracks for Joaquin that missed the U.S., with two of them hitting Canada. The operational (high-resolution) version of the European model is shown in red. Image taken from a custom software package used by TWC.

The ECMWF model is known for its high-quality representation of atmospheric physics and its ability to smoothly incorporate data from a variety of sources. The model is not infallible; back in January, it famously and erroneously predicted that Manhattan would get walloped by several feet of snow, the result of it having placed an upper-level low about 100 miles too far to the west. However, in cases of model disagreement, the ECMWF is often the first to pick up on subtle large-scale features that turn out to be crucial in steering a hurricane or other storm. This was the case during 2012’s Hurricane Sandy, when the ECWMF was ahead of all models in depicting the rare leftward hook into New Jersey that Sandy ended up taking. Two key factors at play with Joaquin are the upper-level low cutting off over the Southeast U.S. and another upper low taking shape well northeast of Joaquin. Most models had projected that the Southeast low would pull Joaquin into its northeast side, a la Sandy, whereas the ECMWF and other models now appear to be reckoning that the upper low in the Atlantic will play a larger role in steering Joaquin.



Figure 7. This WunderMap image shows the GFS-analyzed steering flow at 200 mb (about 40,000 feet) at 06Z (2:00 am EDT) Thursday, October 1, 2015. Joaquin's future track is being shaped by an upper-level low that will cut off from a sharp trough now in the eastern United States (A) and by another upper low developing at the base of another sharp trough in the north central Atlantic (B).


Given the interplay between these two features, it is still too soon to confidently project that Joaquin will remain offshore, but it is fair to say that the ominous HWRF and GFDL tracks are now lower-probability, high-impact possibilities. The strength of Joaquin and the residual disagreement among models calls for continued keen vigilance and careful analysis. Another caveat is that the onshore and offshore forecast tracks do not diverge a great deal until after Friday, so quick action would be needed if the lower-probability onshore solution turned out to be correct.

A key experimental tool for better forecasts missing for Joaquin
One potential aid to making better hurricane track and intensity forecasts is the use of real-time radar data from NOAA's two P-3 hurricane research aircraft. Over the past two years, these aircraft have flown numerous missions into Atlantic hurricanes and tropical storms, sending back real-time radar data that was ingested into the HWRF model, one of our top models for predicting both hurricane tracks and intensities. This real-time data was shown to measurably improve the forecasts from this model. Unfortunately, both NOAA P-3 aircraft are grounded this week for maintenance issues. One aircraft has been undergoing a months-long process to have new wings put on, leaving just one P-3 for this year's hurricane season. Unfortunately, last Friday, de-lamination of that plane's lower fuselage radome, which was deep and too broad to fix at the Aircraft Operation Center's base in Tampa, was discovered. The shell has been trucked to Jacksonville for repair, and the repair will not be done until Friday at the earliest. However, NOAA's jet has been flying upper-level dropsonde missions around the clock, and data from these missions has been getting fed into the models for Joaquin.

Regardless of Joaquin's path, a potentially devastating rain/flood/surge event
Even if Joaquin does stay offshore, a very large pressure gradient between it and a surface high far to the north will keep a broad easterly fetch of wind heading into the U.S. East Coast, leading to a prolonged bout of coastal flooding and erosion over the next several days. Storm-surge expert Hal Needham emphasized the rarity of the situation in a blog post on Thursday morning. “The duration of this wind event is absolutely mind-boggling,” says Needham. Strong, sustained onshore winds (more than 20 mph) could be affecting the mid-Atlantic coast for more than 96 solid hours, regardless of Joaquin’s track. High water will be present for as many as 10 high tides over several days, increasing the risk of erosion and flooding along the coast as well as up to a few miles inland. “This developing situation is truly historic and has not been observed in the modern history of the Mid-Atlantic Coast,” says Needham.

Complicating matters even further, a potentially destructive multi-day bout of heavy rain and inland flooding is on tap, focused on the southern Appalachians and nearby coastal plains, as the cutoff Southeast low continues to pump rich tropical moisture (with at least some contribution from Joaquin’s circulation) over a preexisting frontal zone. Both the ECMWF and GFS model solutions lead to moisture inflow at the 850 mb level (about a mile above sea level) that is close to unprecedented amounts—“off the charts,” as NOAA’s Weather Prediction Center (WPC) put it in a Thursday morning discussion.


Figure 8. 5-day predicted rainfall amounts from 12Z (8 am EDT) Thursday, October 1, to Tuesday, October 6. Image credit: NWS Weather Prediction Center.

Widespread rainfall in recent days (2” – 4” in many areas) has saturated the ground in many areas, which will add to the flood risk. The focus of the heaviest rain may shift from western GA/SC/NC/VA toward the mid-Atlantic toward Sunday and Monday, depending in large part on interactions between the Southeastern upper low and Joaquin. The 5-day rainfall amounts predicted by WPC are astounding: most of the region from northeast Georgia to New Jersey is projected to receive at least 5”, with 15-20” predicted across the bulk of South Carolina. Local amounts are often substantially greater than these large-scale predictions.

The bottom line: regardless of Joaquin’s track, a large and populous part of the United States is in for what could be historic rainfall and a very serious flooding risk.

We’ll have another update later today.

Jeff Masters and Bob Henson

Hurricane

Joaquin Hammers Bahamas; Future Track Still Uncertain

By: Jeff Masters and Bob Henson , 4:05 PM GMT on October 01, 2015

Category 3 Hurricane Joaquin is giving the Central Bahama Islands a ferocious pounding as the storm moves very slowly over the islands. An Air Force hurricane hunter aircraft made two penetrations of Joaquin's center on Thursday morning, and found top surface winds of 125 mph. The central pressure held steady at 942 mb between the two passes at 7:47 and 9:23 am EDT, so Joaquin may have paused in its intensification cycle. The hurricane and a large 36-mile diameter eye that was fully closed in their second pass through. Joaquin took advantage of wind shear that had fallen to the moderate range, 10 - 20 knots, on Thursday morning. Visible and infrared satellite loops show that Joaquin is a moderate-sized hurricane with impressive organization, with a solid core of intense eyewall thunderstorms surrounding a clear eye. Upper level winds analyses from the University of Wisconsin show that the hurricane has maintained an impressive upper-level outflow channel to the southeast, which allowed the hurricane's rapid intensification over the past 24 hours. Ocean temperatures in the region remain a record-warm 30°C (86°F), but may start to cool due to Joaquin's slow motion.


Figure 1. GOES-13 image of Hurricane Joaquin over the Bahamas as seen on Thursday, October 1, 2015, at 10:30 am EDT. At the time, Joaquin had top winds of 125 mph. Image credit: NASA/GSFC.


Figure 2. Winds were rising across the Central Bahamas on Thursday morning, and were a brisk 39 mph, gusting to 58 mph, at 3:13 am EDT at a personal weather station on Exuma Island. Shewp's Webcam from Exuma Island on Thursday morning showed a darkening sky with heavy whitecapping of the waters, as Joaquin approached, but the webcam and weather station stopped reporting at 8:52 am.

Impact of Joaquin on the Bahamas
Joaquin's main threat to the Bahamas is likely to be wind damage. The 11 am Thursday Wind Probability Forecast from NHC gave the highest chances of hurricane-force winds of 69% to San Salvador Island (population 930). Hurricane-force winds are slightly less likely on Cat Island (population 1,500), to the northwest of San Salvador Island. Heavy rains of 10 - 15 inches in the Central Bahamas may also cause considerable flooding damage, as well as the large waves of the storm riding up on top of the expected 5 - 10' storm surge. Thursday morning satellite imagery showed that Joaquin had stalled out over the Central Bahamas; with only a slow motion expected for the next day, the islands will receive and extended pounding, increasing the odds of significant wind damage.


Figure 3. This Maximum Water Depth storm surge image for the Bahamas shows the worst-case inundation scenarios for a Category 3 hurricane with 120 mph winds, as predicted using dozens of runs of NOAA's SLOSH model. For example, if you are inland at an elevation of ten feet above mean sea level, and the combined storm surge and tide (the "storm tide") is fifteen feet at your location, the water depth image will show five feet of inundation. No single storm will be able to cause the level of flooding depicted in this image. The regions of the Bahamas most vulnerable to storm surge tend to lie on the southwest sides of the islands. Since Joaquin is approaching from the northeast, the storm's peak on-shore winds will be affecting the northeast sides of the islands, where deeper offshore waters tend not to allow larger storm surges to build. NHC is forecasting peak water levels (the depth of water above the high tide mark) of 5 - 10 feet from Joaquin in the Bahamas. See wunderground's storm surge pages for more storm surge info.

Outlook for Joaquin: Out to sea?
With favorable conditions for at least the next day (low wind shear and very warm sea-surface temperatures), Joaquin may yet intensify further. The 11 am EDT Thursday advisory from NHC pegs Joaquin’s top sustained winds at 125 mph, and the NHC outlook brings Joaquin to Category 4 status, with top sustained winds of 140 mph projected by Friday. Joaquin is located close to the region where Hurricane Andrew grew from Category 1 to Category 5 status during a year with very suppressed hurricane activity, 1992 (featuring an El Niño event during the first half of the year.) This serves as a reminder that the subtropics can be a worrisome breeding ground for strong hurricanes even during an El Niño year, when activity in the deep tropics tends to be suppressed. We can expect some fluctuation in strength if an eyewall replacement cycle takes hold over the next day or two, as is common after hurricanes go through a rapid intensification phase. Once Joaquin begins moving northward under the influence of stronger upper-level flow, we can expect its top sustained winds to eventually decrease while the size of its wind field increases. The waters are unusually warm across much of the Northwest Atlantic, which may help Joaquin sustain its strength longer than one would otherwise expect.

The track forecast for Joaquin remains low-confidence, although there was an important shift in the 00Z and 06Z Thursday computer-model guidance in favor of keeping Joaquin away from the U.S. East Coast. The global-scale GFS model, which had been predicting a North Carolina landfall for more than a day, shifted in its 00Z Thursday run to a track toward Long Island. The 06Z Thursday run of the GFS showed an even more dramatic shift eastward, with Joaquin hugging the Nova Scotia coastline. Members of the GFS ensemble also reflected this shift, with most but not all of the 06Z GEFS members showing an offshore track. (Ensembles are produced by running a model many times, each with slightly different initial conditions to represent uncertainty in the atmosphere’s starting point.) The UKMET also shifted significantly eastward, moving from a North Carolina landfall in its 12Z Wednesday run to a Cape Cod brushing in its 00Z Thursday run. The high-resolution HWRF and GFDL models stuck to their guns, with their 06Z Thursday runs continuing to depict landfall in North Carolina or Virginia. The 00Z Canadian model also continued to depict a landfall in this region, although it is historically one of the less-reliable track models.
If the trend toward an offshore track holds up in Thursday’s model guidance, kudos must go to the ECMWF model. Its operational run has consistently called for a track well away from the U.S. East Coast, as was the case at 00Z Thursday. Just as significant, most of the ECMWF ensemble members (about 40 out of 50) showed an offshore track in the 00Z Thursday runs, whereas a large part of the ensemble had previously shown of a U.S. landfall. Analyses of the ECMWF ensemble for 12Z Wednesday and 00Z Thursday indicate that the ensemble members who did the best in the first few hours of the forecast were consistently taking Joaquin offshore (see Figure X).


Figure 4. The latest runs from our two top models for forecasting hurricane tracks: the 8 pm EDT Wednesday September 30, 2015 (00Z Thursday) run of the European model (left), and the 2 am EDT October 1 (06Z) run of the GFS model (right) both took Joaquin on a path out to sea that misses the U.S. coast, but were still very far apart. Image credit: wundermap with the "Model Data" layer turned on.





Figure 5. The ensemble runs of our two top models for forecasting hurricane tracks, both run at 8 pm EDT Wednesday September 30, 2015 (00Z Thursday). The 50 members of the European model ensemble (top) had only about 10 of its 50 members that showed a U.S. landfall, while about 10 of the 20 members of the GFS model ensemble (bottom) did so. Compared to the runs done 24 hours previous, the European ensembles had shifted considerably to the east, away from the U.S., with the GFS ensemble members less so. Ensemble runs take the operational version of the model and run it at lower resolution with slightly different initial conditions, to generate an "ensemble" of possible forecasts. 




Figure 6. The European model ensemble run at 8 pm EDT Wednesday September 30, 2015 (00Z Thursday, October 1) had four of its 50 members (grey lines) that tracked the movement of Joaquin exceptionally well during the period 00Z - 12Z October 1. All of these four members had tracks for Joaquin that missed the U.S., with two of them hitting Canada. The operational (high-resolution) version of the European model is shown in red. Image taken from a custom software package used by TWC.

The ECMWF model is known for its high-quality representation of atmospheric physics and its ability to smoothly incorporate data from a variety of sources. The model is not infallible; back in January, it famously and erroneously predicted that Manhattan would get walloped by several feet of snow. However, in cases of model disagreement, the ECMWF is often the first to pick up on subtle large-scale features that turn out to be crucial in steering a hurricane. This was the case during 2012’s Hurricane Sandy, when the ECWMF was ahead of all models in depicting the rare leftward hook into New Jersey that Sandy ended up taking. Two key factors at play with Joaquin are the upper-level low cutting off over the Southeast U.S. and another upper low taking shape well northeast of Joaquin. Most models had projected that the Southeast low would pull Joaquin into its northeast side, a la Sandy, whereas the ECMWF and other models now appear to be reckoning that the upper low in the Atlantic will play a larger role in steering Joaquin.



Figure 7. This WunderMap image shows the GFS-analyzed steering flow at 200 mb (about 40,000 feet) at 06Z (2:00 am EDT) Thursday, October 1, 2015. Joaquin's future track is being shaped by an upper-level low that will cut off from a sharp trough now in the eastern United States (A) and by another upper low developing at the base of another sharp trough in the north central Atlantic (B).


Given the interplay between these two features, it is still too soon to confidently project that Joaquin will remain offshore, but it is fair to say that the ominous HWRF and GFDL tracks are now lower-probability, high-impact possibilities. The strength of Joaquin and the residual disagreement among models calls for continued keen vigilance and careful analysis. Another caveat is that the onshore and offshore forecast tracks do not diverge a great deal until after Friday, so quick action would be needed if the lower-probability onshore solution turned out to be correct.

A key experimental tool for better forecasts missing for Joaquin
One potential aid to making better hurricane track and intensity forecasts is the use of real-time radar data from NOAA's two P-3 hurricane research aircraft. Over the past two years, these aircraft have flown numerous missions into Atlantic hurricanes and tropical storms, sending back real-time radar data that was ingested into the HWRF model, one of our top models for predicting both hurricane tracks and intensities. This real-time data was shown to measurably improve the forecasts from this model. Unfortunately, both NOAA P-3 aircraft are grounded this week for maintenance issues. One aircraft has undergoing a months-long process to have new wings put on, leaving just one P-3 for this year's hurricane season. Unfortunately, last Friday, de-lamination of that plane's lower fuselage radome, which was deep and to broad to fix at the Aircraft Operation Center's base in Tampa, was discovered. The shell has been trucked to Jacksonville for repair, and the repair will not be done until Friday at the earliest. However, NOAA's jet has been flying upper-level dropsonde missions around the clock, and data from these missions has been getting fed into the models for Joaquin.

Regardless of Joaquin's path, a potentially devastating rain/flood/surge event
Even if Joaquin does stay offshore, a very large pressure gradient between it and a surface high far to the north will keep a broad easterly fetch of wind heading into the U.S. East Coast, leading to a prolonged bout of coastal flooding and erosion over the next several days. Storm-surge expert Hal Needham emphasized the rarity of the situation in a blog post on Thursday morning. “The duration of this wind event is absolutely mind-boggling,” says Needham. Strong, sustained onshore winds (more than 20 mph) could be affecting the mid-Atlantic coast for more than 96 solid hours, regardless of Joaquin’s track. High water will be present for as many as 10 high tides over several days, increasing the risk of erosion and flooding along the coast as well as up to a few miles inland. “This developing situation is truly historic and has not been observed in the modern history of the Mid-Atlantic Coast,” says Needham.

Complicating matters even further, a potentially destructive multi-day bout of heavy rain and inland flooding is on tap, focused on the southern Appalachians and nearby coastal plains, as the cutoff Southeast low continues to pump rich tropical moisture (with at least some contribution from Joaquin’s circulation) over a preexisting frontal zone. Both the ECMWF and GFS model solutions lead to moisture inflow at the 850 mb level (about a mile above sea level) that is close to unprecedented amounts—“off the charts,” as NOAA’s Weather Prediction Center (WPC) put it in a Thursday morning discussion.


Figure 8. 5-day predicted rainfall amounts from 12Z (8 am EDT) Thursday, October 1, to Tuesday, October 6. Image credit: NWS Weather Prediction Center.

Widespread rainfall in recent days (2” – 4” in many areas) has saturated the ground in many areas, which will add to the flood risk. The focus of the heaviest rain may shift from western GA/SC/NA/VA toward the mid-Atlantic toward Sunday and Monday, depending in large part on interactions between the Southeastern upper low and Joaquin. The 5-day rainfall amounts predicted by WPC are astounding: most of the region from northeast Georgia to New Jersey is projected to receive at least 5”, with 15-20” predicted across the bulk of South Carolina. Local amounts are often substantially greater than these large-scale predictions.

The bottom line: regardless of Joaquin’s track, a large and populous part of the United States is in for what could be historic rainfall and a very serious flooding risk.

We’ll have another update later today.

Jeff Masters and Bob Henson

Hurricane

Category 3 Joaquin Bears Down on Bahamas

By: Bob Henson , 4:47 AM GMT on October 01, 2015

Hurricane Joaquin got down to business on Wednesday afternoon, vaulting from Category 1 to 3 status in a mere six hours. Joaquin’s top sustained winds zoomed from 85 mph in the 21Z (5:00 pm EDT) advisory from the National Hurricane Center to 115 mph in the 11:00 pm EDT advisory. Since the top winds were only 70 mph on Tuesday night, Joaquin more than qualifies for rapid intensification by the NHC’s definition: an increase in sustained winds of at least 30 knots (35 mph) in 24 hours.

Joaquin is now the second major hurricane of the Atlantic season, joining Hurricane Danny and beating the expectations of seasonal forecasters, as recently as early August, of just one major hurricane in the Atlantic this year (though Danny barely qualified as a major, with winds above that threshold for only a few hours). The current total of 10 named storms is also near the top end of seasonal predictions.


Figure 1. Latest satellite imagery of Hurricane Joaquin from the WU tracking page.

Joaquin still lacks a crisp, well-defined eye on infrared satellite imagery, but its showers and thunderstorms have continued to intensify and consolidate into a large and increasingly symmetric central core. Hurricane-force winds remain confined to a radius of 35 miles from the center of Joaquin, while gales extend out up to 140 miles. The most recent minimal central pressure was 951 millibars, a hefty drop of 37 millibars in roughly 18 hours. Very warm sea-surface temperatures of around 30°C and relatively deep ocean heat content will support even more strengthening over the next couple of days. Hurricane warnings are in effect for the central and northwestern Bahamas, with a hurricane watch for Bimini and Andros Island and a tropical storm warning for the southeastern Bahamas and Andros Island. My Wednesday afternoon update with Jeff Masters has more detail on potential impacts to the Bahamas from this formidable hurricane.

Moderate northerly shear will relax significantly on Thursday into Friday, and it’s possible that Joaquin will have outflow jets helping to ventilate the storm on both its west and east flanks. Together with record-warm SSTs, these factors could help make Joaquin a dangerous Category 4 storm, in line with the latest NHC outlook, which produces peak sustained winds of 140 mph on Thursday night.


Figure 2. Upper-level winds above roughly 35,000 and 55,000 feet (blue flags) show an anticyclonic outflow signature developing over Hurricane Joaquin at 03Z Thursday, October 1 (11:00 pm EDT Wednesday). An outflow jet with wind speeds above 50 knots (58 mph) is funneling from Joaquin toward the southeast, helping to ventilate the storm. Image credit: SSEC/University of Wisconsin.

Some weakening is expected when strong upper-level southerlies begin to impinge on Joaquin’s circulation, especially over the weekend, but Joaquin is likely to remain a potentially damaging hurricane, with a gradually enlarging envelope of high wind, high seas, storm surge, and heavy rain.


Figure 3. Comparison of model projections for Joaquin from 12Z Wednesday. The ECMWF run stands in stark contrast to all other model runs, which are clustered far to the left. The official NHC forecast from Thursday morning (magenta line) splits the difference somewhat. Image credit: Stu Ostro, The Weather Channel.

Forecast update
As we discussed on Wednesday afternoon, most of the computer model runs from 12Z Wednesday pointed toward a landfall for Joaquin somewhere along the coast of North Carolina or southern Virginia. Only the operational ECMWF remained an outlier, taking Joaquin far to sea.

The 18Z suite of guidance did little to change this picture: no ECMWF runs are produced at 18Z, and the other models continued to insist on a U.S. landfall. Early guidance from 00Z Thursday (produced by injecting the most recent data on Joaquin into the 18Z Wednesday model runs) showed little track change, although the projected intensity at landfall is now considerably higher because of Joaquin’s current strength. The complete suite of runs from 00Z Thursday—and in particular the ECMWF run—may help clarify Joaquin’s future, unless of course the ECMWF sticks to its out-to-sea story. The 00Z GFS track was considerably to the right of previous runs, taking Joaquin toward New York and New England, so it appears the picture may remain far more complex than forecasters and residents would prefer.

Most of the dozens of GFS and ECMWF ensemble runs from 12Z Wednesday showed a U.S. landfall, despite the operational ECMWF’s contrariness. (Ensembles are produced by running a model many times, each with slightly different initial conditions to represent uncertainty in the atmosphere’s starting point.) Until we know more, the out-to-sea depiction of the highly skilled ECMWF model must be considered a possibility, as Jeff Masters noted in his WUTV segment on Wednesday evening. At the same time, U.S. coastal residents will need to be getting ready on Thursday for quick action, as it’s possible that a hurricane watch will be posted by NHC as soon as Thursday evening. As of 11:00 pm EDT Wednesday, the official NHC track brings Joaquin into the Delmarva region late Sunday into early Monday.

Jeff Masters and I will have our next update by midday Thursday. We've also launched a live blog on Hurricane Joaquin that will feature updates in between our blog posts.

Bob Henson


Hurricane


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Category 6™

About

Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather